gnu: sdl: Propagate libx11.

* gnu/packages/sdl.scm (sdl): Propagate LIBX11.
  (sdl-gfx, sdl-ttf): Remove LIBX11 from 'inputs'.

gnu: Add SDL extension libraries.

* gnu/packages/sdl.scm (sdl-gfx, sdl-image, sdl-mixer, sdl-net, sdl-ttf): New
  variables.

Merge branch 'master' into core-updates

Conflicts:
	guix/packages.scm

gnu: Add SDL and SDL2.

* gnu/packages/sdl.scm (sdl, sdl2): New variables.

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

Merge branch 'master' into core-updates

gnu: Add libmikmod.

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

Signed-off-by: Andreas Enge <andreas@enge.fr>