file-systems: Allow users to specify file system UUIDs as strings.

Fixes <http://bugs.gnu.org/19778>.
Reported by Mark H Weaver <mhw@netris.org>.

* gnu/system/file-systems.scm (%uuid-rx): New variable.
  (string->uuid): New procedure.
  (uuid): New macro.
* tests/file-systems.scm: New file.
* Makefile.am (SCM_TESTS): Add it.
* doc/guix.texi (File Systems): Give an example of UUID.

file-systems: Implement partition lookup by UUID.

* gnu/build/file-systems.scm (read-ext2-superblock*, partition-predicate): New
  procedures.
  (partition-label-predicate): Rewrite in terms of 'partition-predicate'.
  (partition-uuid-predicate, find-partition-by-uuid, uuid->string): New
  procedures.
  (%network-byte-order): New macro.
  (canonicalize-device-spec)[canonical-title]: Check whether SPEC is a string.
  [resolve]: New procedure.
  Add 'uuid' case and use it.

gnu: nss: Upgrade to 3.19.2.

* gnu/packages/gnuzilla.scm (nss): Upgrade to 3.19.2.

file-systems: Use (guix build syscalls) at build time if needed.

* gnu/build/file-systems.scm: Wrap 'module-use!' statement in 'eval-when'.

gnu: Add rc.

* gnu/packages/rc.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.

gnu: linux-libre: Update to 4.1.2.

* gnu/packages/linux.scm (linux-libre): Update to 4.1.2.

gnu: boost: Patch to avoid -m32 flag on mips.

* gnu/packages/patches/boost-mips-avoid-m32.patch: New file.
* gnu-system.am (dist_patch_DATA): Register patch.
* gnu/packages/boost.scm (boost): Use it.

gnu: boost: Update to 1.58.0.

* gnu/packages/boost.scm (boost): Update to 1.58.0.

substitute: Improve functional decomposition.

* guix/scripts/substitute.scm (display-narinfo-data,
  process-query, process-substitution): New procedures.  Code moved from...
  (guix-substitute): ... here.  Use them.

guix build: Add '--substitute-urls' client option.

* guix/scripts/build.scm (%standard-build-options,
  show-build-options-help): Add --substitute-urls=URLS.
  (set-build-options-from-command-line): Honor it.
* guix/store.scm (%default-substitute-urls): Make public.
* doc/guix.texi (Substitutes): Add xref to the client --substitute-urls
  option.
  (Invoking guix build): Document it.
  (Invoking guix-daemon): Add 'daemon-substitute-urls' anchor.

substitute: Honor "substitute-urls" option passed by "untrusted" clients.

* guix/scripts/substitute.scm (or*): New macro.
  (%cache-url): Honor "untrusted-substitute-urls".
* guix/tests.scm (%test-substitute-urls): New variable.
  (open-connection-for-tests): Use it.
* tests/derivations.scm ("derivation-prerequisites-to-build and substitutes",
  "derivation-prerequisites-to-build and substitutes, non-substitutable
  build", "derivation-prerequisites-to-build and substitutes, local build"):
  Pass it to 'set-build-options'.
* tests/guix-daemon.sh: Likewise.
* tests/store.scm ("substitute query, alternating URLs"): New test.
  ("substitute query", "substitute", "substitute + build-things with output
  path", "substitute, corrupt output hash", "substitute --fallback"): Pass
  #:substitute-urls to 'set-build-options'.

substitute: Store cached narinfo in cache-specific sub-directories.

This ensures that switching between different substitute servers doesn't lead
to a polluted narinfo cache.

* guix/scripts/substitute.scm (narinfo-cache-file): Add 'cache-url'
  parameter.  Add the base32 of CACHE-URL as a sub-directory under
  %NARINFO-CACHE-DIRECTORY.  Update callers.
  (cached-narinfo): Likewise.  Call 'mkdir-p' on the dirname of the cache
  file.  Update callers.
  (remove-expired-cached-narinfos): Add 'directory' parameter and use it
  instead of %NARINFO-CACHE-DIRECTORY.
  (narinfo-cache-directories): New procedure.
  (maybe-remove-expired-cached-narinfo): Call 'remove-expired-cached-narinfos'
  for each item returned by 'narinfo-cache-directories'.

substitute: Pass the cache URL instead of <cache> objects.

* guix/scripts/substitute.scm (<cache>): Rename to...
  (<cache-info>): ... this.
  (open-cache): Rename to...
  (download-cache-info): ... this.  Return a <cache-info> or #f.
  (open-cache*): Remove.
  (cache-narinfo!): Take a URL instead of a <cache> as the first parameter.
  (fetch-narinfos): Likewise.  Call 'download-cache-info'.  Remove use of
  'force'.
  (guix-substitute): Replace calls to 'open-cache*' with %CACHE-URL.

substitute: Remove unneeded conditionals.

* guix/scripts/substitute.scm (guix-substitute): Remove unneeded (if cache
  ...) forms since CACHE is always true (it's a promise.)

gnu: file-systems: Fix typo.

* gnu/system/file-systems.scm (%container-file-systems): Fix typo in a
  comment.

guix lint: Remove duplicated module lines.

* guix/scripts/lint.scm (guix): Remove duplicated lines for using
  'srfi-34' and 'srfi-35' modules.  These lines were introduced twice by
  commits b210b35 and 002c57c.

gnu: Add rhythmbox.

* gnu/packages/gnome.scm (rhythmbox): New variable.

gnu: Add 'libstdc++-doc'.

* gnu/packages/gcc.scm (make-libstdc++-doc): New procedure.
  (libstdc++-doc-4.9, libstdc++-doc-5.1): New variables.

gnu: Add execline.

* gnu/package/skarnet.scm (execline): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu: Add skalibs.

* gnu/package/skarnet.scm (skalibs): New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>