store: 'references/substitutes' really caches its result.

Until now the cache was always empty because 'for-each' was passed ITEMS
as its second argument, and ITEMS was the empty list at that point.

* guix/store.scm (references/substitutes): Add 'requested' variable.
Use it as second argument of 'for-each' in base case.

store: 'references/substitutes' save an RPC is the trivial case.

* guix/store.scm (references/substitutes): Save a
'substitutable-path-info' call when MISSING is empty.

gnu: font-google-noto: Update to 20170403.

* gnu/packages/fonts.scm (font-google-noto): Update to 20170403.
[source]: Update source uri.

gnu: font-gnu-unifont: Update to 10.0.03.

* gnu/packages/fonts.scm (font-gnu-unifont): Update to 10.0.03.
[properties]: Add 'upstream-name' to ease updates.

Revert "gnu: guile-lib: Switch to Guile 2.2."

This reverts commit 66b9183c4f634d9b2ae41176e4eddf0ebb218532.

Revert "gnu: guile-rsvg: Update to commit 05c6a2fd."

This reverts commit 0fd8013fcaafa9f53c7e304b2573c0314471df89.

Revert "gnu: guile-gnome: Update to 2.16.5."

This reverts commit ae5c6ef39378a6fa1f6bf06e8c7f50ab190c485d.

Revert "gnu: guile-cairo: Switch to Guile 2.2."

This commit caused the build of grub-image.png to fail, prevent the
build of grub.cfg and reconfiguring of GuixSD:

<https://bugs.gnu.org/27551>

This reverts commit e3ddb1e83296c10338d35bc687772242b2f5eac6.

gnu: guile-git: Update source URL.

* gnu/packages/guile.scm (guile-git)[source]: Update URL.

guix: git: Stop using libgit2-shutdown.

* guix/git.scm (with-libgit2): Stop calling (libgit2-shutdown) to prevent
segfaults when pointer finalizers are run.

gnu: cd-hit: Update to 4.6.8.

* gnu/packages/bioinformatics.scm (cd-hit): Update to 4.6.8.

gnu: bwa: Update to 0.7.15.

* gnu/packages/bioinformatics.scm (bwa): Update to 0.7.15.

gnu: btrfs-progs: Update to 4.11.1.

* gnu/packages/linux.scm (btrfs-progs): Update to 4.11.1.

gnu: tor: Update to 0.3.0.9 [fixes CVE-2017-0377].

* gnu/packages/tor.scm (tor): Update to 0.3.0.9.

gnu: Add emacs-exwm-x.

* gnu/packages/emacs.scm (emacs-exwm-x): New variable.

gnu: Add emacs-switch-window.

* gnu/packages/emacs.scm (emacs-switch-window): New variable.

gnu: guile-cairo: Switch to Guile 2.2.

This patch adjusts dependent packages accordingly.

* gnu/packages/gtk.scm (guile-cairo)[inputs]: Switch to GUILE-2.2 and
GUILE-LIB.
(guile-rsvg)[inputs]: Likewise.
(guile-present)[inputs]: Likewise.
(guile-gnome)[inputs]: Likewise.
* gnu/packages/plotutils.scm (guile-charting)[inputs]: Switch go
GUILE-2.2.

gnu: guile-gnome: Update to 2.16.5.

* gnu/packages/gtk.scm (guile-gnome): Update to 2.16.5.
[arguments] <pre-configure>: Use @GUILE_EFFECTIVE_VERSION@ instead of
"2.0".
[properties]: New field.

gnu: guile-rsvg: Update to commit 05c6a2fd.

* gnu/packages/gtk.scm (guile-rsvg): Update to commit 05c6a2fd.
[source](url): Change to gitlab.com.
(snippet): Use @GUILE_EFFECTIVE_VERSION@ instead of "2.0".
* gnu/packages/patches/guile-rsvg-pkgconfig.patch: Use
"$GUILE_EFFECTIVE_VERSION" instead of "2.0".

gnu: guile-lib: Switch to Guile 2.2.

* gnu/packages/guile.scm (guile-lib)[inputs]: Replace GUILE-2.0 with
GUILE-2.2.
(guile2.0-lib): New variable.
(guile2.2-lib): Mark as deprecated.
* gnu/packages/guile.scm (guile-ics): Use GUILE2.0-LIB.
* gnu/packages/gtk.scm (guile-cairo, guile-rsvg)
(guile-present, guile-gnome): Likewise.
* gnu/packages/skribilo.scm (skribilo): Likewise.