Merge branch 'master' into core-updates

store: Add 'hash-part->path'.

* guix/store.scm (hash-part->path): New procedure.
* tests/store.scm ("hash-part->path"): New test.

offload: Fix 'choose-build-machine' for several machines.

* guix/scripts/offload.scm (choose-build-machine)[undecorate]: Turn into
  a two-argument procedure.

offload: Convert the port number to a string when invoking lsh.

* guix/scripts/offload.scm (remote-pipe, send-files): Pass the result of
  'build-machine-port' to 'number->string'.

offload: Allow build machines to specify a port number.

* guix/scripts/offload.scm (<build-machine>): Add 'port' field.
  (remote-pipe, send-files): Use lsh's '-p' option when invoking it.

guix build: Support '--with-source' along with '-e'.

* guix/scripts/build.scm (derivation-from-expression): Remove.
  (options->derivations): Handle pairs of the form
  "('argument . (? derivation?))".
  (options/resolve-packages): Add 'store' parameter; update caller.  Add
  'system' variable.  Add case for 'expression pairs.
* guix/scripts/archive.scm (derivation-from-expression): New procedure.

guix build: Add '--with-source'.

* guix/scripts/build.scm (package-with-source): New procedure.
  (show-help): Add '--with-source'.
  (%options): Likewise.
  (options->derivations): Call 'options/with-source' and
  'options/resolve-packages'.
  (options/resolve-packages, options/with-source): New procedures.
* doc/guix.texi (Invoking guix build): Document '--with-source'.

download: 'download-to-store' accepts plain file names.

* guix/download.scm (download-to-store): When URI is #f, assume that URL
  is a file name, and handle it.

More /gnu/store replacements.

* gnu/packages/gcc.scm (gcc-4.7): Change /nix/store in comment.
* gnu/system/vm.scm (operating-system-default-contents):
  Use (%store-prefix) instead of "/nix/store".
* guix/derivations.scm (derivation-path->output-path,
  derivation-path->output-paths): Change to /gnu/store in docstring.

Change default store values from /nix/store to /gnu/store.

* gnu/packages/ld-wrapper.scm (%store-directory): Change the default to
  /gnu/store.
* guix/build/utils.scm (%store-directory): New procedure.
  (remove-store-references): Use it for the default value of 'store'.
* guix/packages.scm (patch-and-repack)[builder]: Change default store to
  /gnu/store.

Merge branch 'master' into core-updates

gnu: linux-initrd: Make the pseudo-tty device nodes.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Create
  /dev/ptmx and /dev/pts.
* gnu/system/vm.scm (qemu-image): Umount /fs/dev/pts before /fs.

offload: Honor absolute build timeouts.

* guix/scripts/offload.scm (offload): Remove default value for
  'build-timeout'.  Pass '--timeout' to the remote 'guix build'
  process.
  (transfer-and-offload, process-request): Remove default value for
  'build-timeout'.

guix build: Add '--timeout' to the common build options.

* guix/scripts/build.scm (show-build-options-help): Document
  '--timeout'.
  (set-build-options-from-command-line): Pass #:timeout to
  'set-build-options'.
  (%standard-build-options): Add '--timeout'.
* doc/guix.texi (Invoking guix build): Document it.

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.

build: Change state and log directories to $localstatedir/.../guix.

* daemon.am (libstore_a_CPPFLAGS): Change /nix to /guix.
* guix/config.scm.in (%state-directory): Likewise.
* guix/store.scm (log-file): Likewise.

offload: Move macro definitions before use.

* guix/scripts/offload.scm (lock-file, unlock-file, with-file-lock,
  with-machine-lock, machine-slot-file, acquire-build-slot,
  release-build-slot): Move definitions above their first use.

offload: Distinguish between 'decline' and 'postpone'.

* guix/scripts/offload.scm (transfer-and-offload): New procedure, with
  core formerly in 'process-request'.
  (choose-build-machine): Remove 'requirements' parameter.
  (process-request): Reply 'decline' when none of MACHINES matches the
  requirements, and 'postpone' when MACHINES are busy.

offload: Prevent locked files from being GC'd.

* guix/scripts/offload.scm (%slots): New variable.
  (choose-build-machine): Add SLOT to '%slots'.

offload: Fix thinko.

* guix/scripts/offload.scm (choose-build-machine)[machine+slots]: Use
  'filter-map', not 'filter'.