gnu: Add yelp.

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

gnu: Add yelp-xsl.

* gnu/packages/gnome.scm (yelp-xsl): New variable.

download: Keep only 2 store items for all the downloads.

This significantly reduces churn in the store.  It also reduces run time
of 'guix build inkscape -Sd' by ~10%.

* guix/download.scm (url-fetch)[mirror-file]: New variable.
  [builder]: Get URL from the "guix download url" env. var.  Get the mirrors
  from MIRROR-FILE.  Pass #:script-name and #:env-vars to 'gexp->derivation'.

gexp: Add #:script-name parameter to 'gexp->derivation'.

* guix/gexp.scm (gexp->derivation): Add #:script-name parameter.
* doc/guix.texi (G-Expressions): Document it.

monads: Inline the procedure returned by liftN.

* guix/monads.scm (define-lift): Turn into a macro that open-codes the result
  of its lift.

gnu: shadow: Update to 4.2.1.

* gnu/packages/admin.scm (shadow): Update to 4.2.1.
  [source]: Use the release tarball.

gnu: Add abduco.

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

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

gnu: Add cabal-install.

* gnu/packages/haskell.scm (cabal-install): New variable.

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

gnu: conky: Fix license.

* gnu/packages/conky.scm (conky)[license]: Set to LICENSE:GPL3+.

gnu: services: Add nginx-service.

* gnu/services/web.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* guix.texi ("Web Services"): New section.

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.

import: pypi: Move generally useful procedures to utils module.

* guix/import/pypi.scm (make-pypi-sexp): Factorize license to symbol
  conversion code.
  (string->license, snake-case, guix-hash-url): Move from here...
* guix/import/utils.scm: ... to here.
  (license->symbol): New procedure.

gnu: Add ruby-arel.

* gnu/packages/ruby.scm (ruby-arel): New variable.

gnu: Add conky.

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

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

gnu: lua: Add patch to generate pkg-config file.

* gnu/packages/patches/lua-pkgconfig.patch: New file.
* gnu/packages/lua.scm (lua)[source]: Add patch.
* gnu-system.am (dist_patch_DATA): Register patch.

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

Thank Eric Hanchrow.

emacs: Add completions for 'guix graph'.

* emacs/guix-pcomplete.el (guix-pcomplete-parse-linter-regexp): Improve
  and rename to ...
  (guix-pcomplete-parse-list-regexp): ...this.  New variable.
  (guix-pcomplete-lint-checkers): Use it.
  (guix-pcomplete-graph-types): New function.
  (guix-pcomplete-complete-command-arg): Complete package names for
  'guix graph' command.
  (guix-pcomplete-complete-option-arg): Complete '-t/--type' option.

gnu: git-modes: Update to 1.2.0.

* gnu/packages/emacs.scm (git-modes): Update to 1.2.0.
  [arguments]: Disable tests.

gnu: magit-svn: Update to 2.1.0.

* gnu/packages/emacs.scm: Use (gnu packages base) module.  Remove
  duplicated (gnu packages guile) and (gnu packages linux) modules.
  (magit-svn): Update to 2.1.0.
  [source]: Use 'url-fetch' method.
  [inputs]: Remove.  Move "emacs" to 'native-inputs', move "magit" to
  'propagated-inputs'.
  [native-inputs]: Add "tar" and "gzip".
  [propagated-inputs]: Add "dash".
  [arguments]: Adjust builder for the new inputs and unpacking the source.

gnu: magit: Update to 2.2.1.

* gnu/packages/emacs.scm (magit): Update to 2.2.1.
  [inputs]: Remove 'git:gui'.
  [propagated-inputs]: Add 'dash', remove 'git-modes'.
  [arguments]: Add PREFIX and DASH_DIR to 'make-flags'.  Remove
  'configure', 'augment-load-path' and 'post-install' phases.