gnu: rxvt-unicode: Install the terminal capability data.

This provides the necessary terminal capability data, which are required
by ncurses-based applications.

* gnu/packages/xdisorg.scm (rxvt-unicode)[native-inputs]: Add ncurses.
[arguments]: Set the destination of the terminfo files.
[native-search-path]: New field.  Make them automatically available to
the user.

gnu: msmtp: Update to 1.6.3.

* gnu/packages/mail.scm (msmtp): Update to 1.6.3.
[inputs]: Add libsecret.

gnu: claws-mail: Update to 3.13.1.

* gnu/packages/mail.scm (claws-mail): Update to 3.13.1.

gnu: python-cython: Update to 0.23.4.

* gnu/packages/python.scm (python-cython): Update to 0.23.4.

gnu: ruby: Update to 2.2.4.

This version fixes CVE-2015-7551.

* gnu/packages/ruby.scm (ruby): Update to 2.2.4.

packages: Remove now redundant graph procedures.

These procedures are now redundant with those in (guix graph) and are no
longer used since commit a51cbecb.

* gnu/packages.scm (vhash-refq, package-dependencies)
(package-direct-dependents, package-transitive-dependents)
(package-covering-dependents): Remove.

gnu: offlineimap: Update to 6.6.0.

* gnu/packages/mail.scm (offlineimap): Update to 6.6.0.

gnu: gnupg: Update to 1.4.20.

* gnu/packages/gnupg.scm (gnupg-1): Update to 1.4.20.

gnu: Add gnome-shell.

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

gnu: Add gnome-control-center.

* gnu/packages/gnome.scm (gnome-control-center): New variable.

gnu: Add gnome-bluetooth.

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

gnu: Add libgtop.

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

gnu: Add colord-gtk.

* gnu/packages/freedesktop.scm (colord-gtk): New variable.

gnu: Add telepathy-logger.

* gnu/packages/freedesktop.scm (telepathy-logger): New variable.

gnu: tilda: Update to 1.3.1.

* gnu/packages/terminals.scm (tilda): Update to 1.3.1.

gnu: Add tlsdate.

* gnu/packages/ntp.scm (tlsdate): New variable.

gnu: mpv: Update to 0.14.0.

* gnu/packages/video.scm (mpv): Update to 0.14.0.

gnu: mpv: Fix build by using pkg-config for smbclient.

This is a followup to commit 710964d.

* gnu/packages/video.scm (mpv)[arguments]: Remove 'patch-wscript' phase.

gnu: agg: Update URLs.

* gnu/packages/graphics.scm (agg)[source, home-page]: Add up-to-date
URLs.

gnu: Use #:prefix when importing (guix licenses).

This works around a problem with #:hide, whereby Guile would report
'zlib', 'openssl', and/or 'expat as colliding bindings at run time
despite the #:hide.

* gnu/packages/linux.scm: Use #:prefix license for (guix licenses).
* gnu/packages/haskell.scm: Likewise.