gnu: Add 'version-prefix' and 'version-major+minor'; use them.

The procedure version-prefix truncates a version string to a certain
number of components. version-major+minor is a special case of this,
which extracts the "major.minor" part of the string. Previously this
was handled by an expression common to several packages.

* guix/utils.scm (version-prefix, version-major+minor): New procedures
* gnu/packages/backup.scm (duplicity): Use version-major+minor.
* gnu/packages/cmake.scm (cmake): Likewise.
* gnu/packages/gnome.scm (libbonobo, libbonoboui): Likewise.
* gnu/packages/gnutls.scm (gnutls): Likewise.
* gnu/packages/mail.scm (gmime): Likewise.
* gnu/packages/mpd.scm (mpd): Likewise.
* gnu/packages/mpi.scm (openmpi): Likewise.

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

Merge branch 'master' into core-updates

Conflicts:
	gnu/packages/image.scm

gnu: Consolidate databases in (gnu packages databases).

* gnu/packages/databases.scm: New file, with the contents of the
  following deleted files.
* gnu/packages/mysql.scm, gnu/packages/postgresql.scm,
  gnu/packages/recutils.scm, gnu/packages/sqlite.scm,
  gnu/packages/bdb.scm: Remove.
* gnu-system.am (GNU_SYSTEM_MODULES): Adjust accordingly.
* gnu/packages/apl.scm, gnu/packages/dc.scm, gnu/packages/games.scm,
  gnu/packages/gnunet.scm, gnu/packages/linux.scm, gnu/packages/mail.scm,
  gnu/packages/mpd.scm, gnu/packages/nvi.scm, gnu/packages/openldap.scm,
  gnu/packages/package-management.scm, gnu/packages/python.scm,
  gnu/packages/qt.scm, gnu/packages/rdf.scm,
  gnu/packages/version-control.scm: Adjust to new module name.

Merge branch 'master' into core-updates

gnu: Fix synopses for emacs-wget and fetchmail.

* gnu/packages/emacs.scm (emacs-wget): Improve synopsis.
* gnu/packages/mail.scm (fetchmail): Fix typo in synopsis.

gnu: notmuch: Update to 0.18.1.

* gnu/packages/mail.scm (notmuch): Update to 0.18.1.

Merge branch 'master' into core-updates

gnu: Adjust more packages to GLib "bin" split.

* gnu/packages/gimp.scm (gegl): Add glib:bin to 'native-inputs'.
* gnu/packages/mail.scm (mu): Ditto.

gnu: Add notmuch.

* gnu/packages/mail.scm (notmuch): New variable.

Merge branch 'master' into core-updates

gnu: offlineimap: fix license.

* gnu/packages/mail.scm (offlineimap) [license]: Change to gpl2+.

gnu: Add mu.

* gnu/packages/mail.scm (mu): New variable.

gnu: Add offlineimap

* gnu/packages/mail.scm (offlineimap): New variable.

gnu: mailutils: Build against Readline 6.2.

* gnu/packages/mail.scm (mailutils): Use Readline 6.2.

gnu: mutt: Upgrade to 1.5.23.

* gnu/packages/mail.scm (mutt): Upgrade to 1.5.23.  Add bitbucket
  source URL and try it first.

gnu: Add Bogofilter.

* gnu/packages/mail.scm (bogofilter): New variable.

Merge branch 'master' into core-updates

Conflicts:
	gnu-system.am

gnu: gmime: Use gnome mirror for download.

* gnu/packages/mail.scm (gmime): Use gnome mirror, fixes download problems
    with automatic https redirection.

gnu: Add gmime.

* gnu/packages/mail.scm (gmime): New variable.

gnu: Synchronize descriptions with 'gnumaint'.