import: Add Ruby gem importer.

* gnu/scripts/import.scm (importers): Add "gem".
* gnu/import/gem.scm: New file.
* gnu/scripts/import/gem.scm: New file.
* Makefile.am (MODULES): Add them.
* guix.texi ("invoking guix import"): Document it.

Add 'guix graph'.

* guix/scripts/graph.scm, tests/graph.scm, tests/guix-graph.sh,
  doc/images/coreutils-bag-graph.dot, doc/images/coreutils-graph.dot: New
  files.
* Makefile.am (MODULES): Add guix/scripts/graph.scm.
  (SH_TESTS): Add tests/guix-graph.sh.
  (SCM_TESTS): Add tests/graph.scm.
* doc.am (DOT_FILES, DOT_VECTOR_GRAPHICS): New variables.
  (EXTRA_DIST): Use them.
  (dist_infoimage_DATA): Use $(DOT_FILES).
  (pdf-local, info-local, ps-local): Likewise.
* doc/guix.texi (Packages with Multiple Outputs): Add cross-reference to 'guix
  graph'.
  (Invoking guix gc): Likewise.
  (Invoking guix graph): New section.

scripts: package: Add --install-from-file option.

* guix/scripts/package.scm (show-help): Add help text for --install-from-file
  option.
  (%options): Add --install-from-file option.
* tests/guix-package.sh: Test it.
* doc/guix.texi ("invoking guix package"): Document it.
* doc/package-hello.scm: New file.
* doc.am (EXTRA_DIST): Add it.

size: Get the item's size from the daemon rather than compute it.

This removes all I/O, which obviously makes things faster.

* guix/scripts/size.scm (file-size, store-item-exists?): Remove.
  (query-path-info*): New procedure.
  (file-size*): Rename to...
  (file-size): ... this; adjust caller.  Use 'query-path-info*' instead of
  'file-size'.

lint: Add 'formatting' checker.

* guix/scripts/lint.scm (report-tabulations, report-trailing-white-space,
  report-long-line, report-formatting-issues, check-formatting): New
  procedures.
  (%formatting-reporters): New variable.
  (%checkers): Add 'formatting' checker.
* tests/lint.scm ("formatting: tabulation", "formatting: trailing white
  space", "formatting: long line", "formatting: alright"): New tests.
* doc/guix.texi (Invoking guix lint): Mention the 'formatting' checker.

import: elpa: Fix typo.

Reported by Eric Dvorsak <eric@dvorsak.fr> on #guix.

* guix/scripts/import/elpa.scm (%default-options): Remove redundant
  quote which led to an error if --archive option was not specified.

Fix typos in translatable strings.

Reported by Anders Jonsson <anders.jonsson@norsjovallen.se>.

* gnu/packages/backup.scm, gnu/packages/databases.scm,
  gnu/packages/linux.scm, gnu/packages/perl.scm,
  gnu/packages/web.scm, guix/scripts/lint.scm,
  guix/scripts/publish.scm: Fix typos in translatable strings.

size: Add '--substitute-urls' option.

* guix/scripts/size.scm (show-help, %options): Add --substitute-urls.
  (%default-options): Add 'substitute-urls'.
  (guix-size): Honor it.
* doc/guix.texi (Invoking guix size): Document it.

import: hackage: Remove reference to unbound variable.

* guix/scripts/import/hackage.scm (guix-import-hackage): Fix error message for
  imports from stdin, which referred to unbound variable 'package-name'.

size: Remove leftover 'pk'.

* guix/scripts/size.scm (profile->page-map): Remove leftover 'pk'.

publish: Do not load archive content in memory.

Previously, before replying to a /nar/* request, 'guix publish' would first
build up the whole nar into memory (as a consequence of
<http://bugs.gnu.org/21093>), which obviously doesn't scale.

* guix/scripts/publish.scm (render-nar): Return STORE-PATH instead of a
  procedure that calls 'write-file'.
  (sans-content-length): New procedure.
  (http-write): For 'x-nix-archive', don't call '%http-write'.  Instead, call
  'write-file' right from here, using BODY as the file name.

Merge branch 'master' into core-updates

publish: Serve /nar requests in a separate thread.

* guix/scripts/publish.scm (%http-write): New variable.
  (http-write): New procedure.
  (concurrent-http-server): New variable.
  (run-publish-server): Use it.

publish: Write hashes in nix-base32 format.

* guix/scripts/publish.scm (narinfo-string): Use
  'bytevector->nix-base32-string', not 'bytevector->base32-string'.

system: Add 'kernel-arguments' field.

* gnu/system.scm (<operating-system>)[kernel-arguments]: New field.
  (operating-system-grub.cfg): Honor it.
  (operating-system-parameters-file): Add 'kernel-arguments' to the parameters
  file.
* guix/scripts/system.scm (previous-grub-entries)[system->grub-entry]: Read
  the 'kernel-arguments' field of the parameters file, when available.
* gnu/system/vm.scm (system-qemu-image/shared-store-script):
  Use (operating-system-kernel-arguments os) in '-append'.
* doc/guix.texi (operating-system Reference): Document it.

size: Gracefully handle EPIPE.

* guix/scripts/size.scm (guix-size): Wrap body in 'leave-on-EPIPE'.

ui: Add 'leave-on-EPIPE'.

* guix/scripts/package.scm (leave-on-EPIPE): Move to...
* guix/ui.scm (leave-on-EPIPE): ... here.

Merge branch 'master' into core-updates

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.