gnu: Move pkg-config to 'native-inputs' in various places.

* gnu/packages/glib.scm (libsigc++): Move pkg-config to
  'native-inputs'.
  (glibmm): Likewise.
* gnu/packages/mpd.scm (mpd): Likewise.
* gnu/packages/package-management.scm (guix-0.7): Likewise.
* gnu/packages/sdl.scm (sdl-net): Likewise.
  (sdl-ttf): Likewise.
* gnu/packages/xiph.scm (vorbis-tools): Likewise.

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-system.am

gnu: Adjust synopses as recommended by 'guix lint'.

Remove leading articles and trailing periods in package synopses.

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.

gnu: Add ncmpcpp.

* gnu/packages/mpd.scm (ncmpcpp): New variable.

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

Merge branch 'master' into core-updates

gnu: libmpdclient: Add native input doxygen.

* gnu/packages/mpd.scm (libmpdclient): Add native input doxygen.

Merge branch 'master' into core-updates

gnu: Add ncmpc.

* gnu/packages/mpd.scm (ncmpc): New variable.

Merge branch 'master' into core-updates

Conflicts:
	gnu/packages/libwebsockets.scm

gnu: Add mpd.

* gnu/packages/mpd.scm (mpd): New variable.

gnu: Add libmpdclient.

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