store: Document `add-to-store' hack for `fixed?'.

* guix/store.scm (add-to-store): Document that `fixed?' must be #t.

store: Add `store-path-package-name'.

* guix/store.scm (store-path-package-name): New procedure.
* tests/utils.scm ("store-path-package-name"): New test.

guix-build: Add `--root'.

* guix/store.scm (add-indirect-root): New operation.
* guix-build.in (show-help): Document `--root'.
  (%options): Add `--root'.
  (guix-build)[register-root]: New procedure.  Call it when `--root' is
  passed.

store: Add `query-path-hash'.

* guix/store.scm (write-arg, read-arg): Add `base16' literal and
  corresponding rule.
  (query-path-hash): New operation.

* tests/derivations.scm ("fixed-output derivation"): Check whether
  `query-path-hash' returns a bytevector.

distro: Add a statically-linked, relocatable Guile 2.0 package.

* distro/packages/base.scm (%guile-static, %guile-static-stripped): New
  variables.

* distro/patches/guile-relocatable.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.

Optimize `store-path?'.

* guix/store.scm (store-path?): Check with `string-prefix?' instead of a
  regexp.

Add `close-connection'.

* guix/store.scm (close-connection): New procedure.

Upgrade Nix worker protocol.

We were already relying on the new version in `set-build-options', so
this patch fixes that.

* guix/store.scm (%protocol-version): Increase.
  (open-connection)[reserve-space?]: New argument.  Pass it to the
  server when it's recent enough.

Add the `valid-path?' RPC.

* guix/store.scm (valid-path?): New procedure.

* tests/builders.scm ("http-fetch", "gnu-build"): Use it.
* tests/derivations.scm ("add-to-store, flat", "add-to-store,
  recursive", "derivation with no inputs", "build derivation with 1
  source", "build derivation with coreutils",
  "build-expression->derivation with expression returning #f"):
  Likewise.

Add missing `set-build-options' parameters.

* guix/store.scm (set-build-options)[build-cores, use-substitutes?]: New
  keyword parameters.
  [send]: Change to expect a type, and use `write-arg'.
  Send settings for BUILD-CORES and USE-SUBSTITUTES? when the server
  supports it.

store: Wait for the server to be done sending output.

* guix/store.scm (current-build-output-port): New variable.
  (process-stderr): Add docstring.  Always return #f, except upon
  %STDERR-LAST.  Upon %STDERR-NEXT, write to
  `current-build-output-port', not `current-error-port'.
  (set-build-options): Loop until `process-stderr' returns true.
  (define-operation): Likewise.
  (build-derivations): Update docstring to mention that it's
  synchronous.

Add `add-to-store' with recursive directory storage.

* guix/store.scm (write-file): Implement directory recursive dump.
  (add-to-store): Fix the parameter list.

* tests/derivations.scm (directory-contents): New procedure.
  ("add-to-store, recursive"): New test.

First stab at the `derivation' primitive.

* guix/store.scm (%store-prefix): New parameter.
  (store-path?, derivation-path?): New procedures.

* guix/derivations.scm (write-derivation): Pass SOURCES through
  `object->string'.
  (compressed-hash, store-path, output-path, derivation): New
  procedures.

* tests/derivations.scm (%store): New global variable.
  ("derivation with no inputs"): New test.

store: Raise error conditions upon protocol errors.

* guix/store.scm (&nix-error, &nix-protocol-error): New SRFI-35
  condition types.
  (process-stderr): Raise an error condition upon protocol errors
  instead of returning to the caller.  This allows the connection to be
  reused for further interactions.

Split (guix) in (guix store) and (guix derivations).

* guix.scm: Move contents to other files.  Just aggregate these.
* guix/derivations.scm, guix/store.scm: New files.