tests: 'topologically-sorted' test handles different references orders.

* tests/store.scm ("topologically-sorted, more difficult"): Arrange to
  handle a different ordering of (references %store y).

store: Add #:timeout build option.

* guix/serialization.scm (write-string-pairs): New procedure.
* guix/store.scm (write-arg): Add 'string-pairs' case.
  (set-build-options): Add 'timeout' keyword parameter.  Honor it.
* tests/derivations.scm ("build-expression->derivation and timeout"):
  New test.

utils: Add a non-blocking option for 'fcntl-flock'.

* guix/utils.scm (F_SETLK): New variable.
  (fcntl-flock): Add 'wait?' keyword parameter; honor it.
* tests/utils.scm ("fcntl-flock non-blocking"): New test.

store: 'export-paths' doesn't export references of the given files.

This fixes a regression introduced in
99fbddf9a623757e39d88bfb431f8f7d6f24b75b ("store: Change 'export-paths'
to always export in topological order.")

* guix/store.scm (export-paths): Define 'ordered' variable.  Iterate
  over it.
* tests/store.scm ("export/import paths, ensure topological order"): Add
  'file0'.  Adjust accordingly.

tests: Rewrite 'fcntl-lock' test.

* tests/utils.scm (temp-file): New variable.
  ("fcntl-flock"): Rewrite to actually test whether the child process
  waits for the lock to be released.  The previous test was wrong
  because (1) it expected F_SETLK semantics, not F_SETLKW, and (2) it
  got EBADF because of a mismatch between the open mode and the lock
  style.

nar: Produce archives with files sorted in C collation order.

* guix/nar.scm (write-file) <directory>: Pass 'string<?' as the second
  argument to 'scandir'.
* tests/nar.scm ("write-file puts file in C locale collation order"):
  New test.

derivations: Add support for recursive fixed-output derivations.

* guix/derivations.scm (<derivation-output>): Add 'recursive?' field.
  Adjust 'make-derivation-output' callers.
  (%read-derivation) <fixed-output>: When HASH-ALGO starts with 'r:',
  set the 'recursive?' field and drop 'r:' from the hash algo name.
  (write-derivation)[write-output]: Write the algo as 'r:HASH-ALGO' when
  the RECURSIVE? field is set.
  (derivation-hash) <fixed-output>: Prepend "r:" when RECURSIVE? is set.
  (fixed-output-path): New procedure.
  (derivation): Add #:recursive? parameter.  Use 'fixed-output-path' to
  compute the output file name of a fixed output derivation.
  (build-expression->derivation): Add #:recursive? parameter.  Pass it
  to 'derivation'.
* tests/derivations.scm ("fixed-output derivation, recursive",
  "build-expression->derivation produces recursive fixed-output",
  "build-expression->derivation uses recursive fixed-output"): New
  tests.
* doc/guix.texi (Derivations): Document #:recursive? for 'derivation'.
  Add #:recursive? for 'build-expression->derivation'.

guix hash: Add '--recursive'.

* guix/scripts/hash.scm (show-help): Add --recursive.
  (%options): Likewise.
  (guix-hash)[file-hash]: New procedure.  Honor --recursive.
  Use it.
* guix/nar.scm (write-file): Add missing field to the &nar-error
  condition raised upon unsupported file type; change its message to be
  more descriptive.
* tests/guix-hash.sh: Add tests with -r.
* doc/guix.texi (Invoking guix hash): Document --recursive.

nar: 'write-file' can write to non-file ports.

* guix/nar.scm (write-contents): Use 'sendfile' only when P is a file
  port.
* tests/nar.scm ("write-file supports non-file output ports"): New test.

store: Change 'export-paths' to always export in topological order.

* guix/store.scm (export-paths): Pass PATHS through
  'topologically-sorted' before iterating.
* tests/store.scm ("export/import paths, ensure topological order"): New
  test.

monads: Add 'text-file*'.

* guix/monads.scm (text-file*): New procedure.
* tests/monads.scm ("text-file*"): New test.
* doc/guix.texi (The Store Monad): Change example since the previous one
  would erroneously fail to retain a reference to Coreutils.  Document
  'text-file*'.

store: Add 'topologically-sorted'.

* guix/store.scm (topologically-sorted): New procedure.
* tests/store.scm ("topologically-sorted, one item",
  "topologically-sorted, several items", "topologically-sorted, more
  difficult"): New tests.

nar: Add 'restore-file-set', for use by build hooks.

* guix/nar.scm (&nar-invalid-hash-error, &nar-signature-error): New
  condition types.
  (&nar-error): Add 'file' and 'port' fields.
  (&nar-read-error): Remove 'port' and 'file' fields.
  (lock-store-file, unlock-store-file, finalize-store-file,
  temporary-store-directory, restore-file-set): New procedures.
* tests/nar.scm (%seed): New variable.
  (random-text): New procedure.
  ("restore-file-set (signed, valid)", "restore-file-set (missing
  signature)", "restore-file-set (corrupt)"): New tests.
* po/Makevars (XGETTEXT_OPTIONS): Add '--keyword=message'.nar fixes
* po/POTFILES.in: Add guix/nar.scm.

hash: Add 'open-sha256-input-port', for Guile > 2.0.9.

* guix/hash.scm (open-sha256-input-port): New procedure.
* tests/hash.scm (supports-unbuffered-cbip?): New procedure.
  ("open-sha256-input-port, empty", "open-sha256-input-port, hello",
  "open-sha256-input-port, hello, one two",
  "open-sha256-input-port, hello, read from wrapped port"): New tests.

utils: Add 'fcntl-flock'.

* guix/utils.scm (%struct-flock, F_SETLKW, F_xxLCK): New variables.
  (fcntl-flock): New procedure.
* tests/utils.scm ("fcntl-flock"): New test.

store: Add 'register-path' procedure.

* guix/store.scm (register-path): New procedure.
* tests/store.scm ("register-path"): New test.
* guix/config.scm.in (%guix-register-program): New variable.
* configure.ac: Compute and substitute 'guix_sbindir'.  Compute
  'guix_prefix'.
* pre-inst-env.in: Define 'GUIX_REGISTER'.

guix-register: Support registration in the current store, without '--prefix'.

* nix/guix-register/guix-register.cc (register_validity): Leave
  'info.path' unmodified when PREFIX is empty.
  (main): Call 'settings.processEnvironment' early on.
  Leave 'settings.nixStore' unmodified when PREFIX is empty.

archive: Add '--missing'.

* guix/scripts/archive.scm (show-help, %options): Add '--missing'.
  (guix-archive)[lines]: New procedure.
  Use it to honor '--missing'.
* tests/guix-archive.sh: Add tests.
* doc/guix.texi (Invoking guix archive): Document '--missing'.

guix package: Gracefully deal with EPIPE on stdout for --list-*.

* guix/scripts/package.scm (leave-on-EPIPE): New macro.
  (guix-package): Use it for 'list-installed', 'list-available', and
  '--list-generations'.
* tests/guix-package.sh: Add test.

archive: Add '--authorize'.

* guix/scripts/archive.scm (authorize-key): New procedure.
  (guix-archive): Call it when OPTS contains 'authorize-key'.
* tests/guix-archive.sh: Add test with invalid public key.
* guix/pki.scm: Export '%acl-file'.
* doc/guix.texi (Invoking guix archive): Make it clear that '--import'
  works only with authorized keys.  Document '--authorize'.