gnu: inkscape: Use libgc 7.2.

* gnu/packages/inkscape.scm (inkscape): Use LIBGC-7.2 instead of LIBGC.

Merge branch 'master' into core-updates

Conflicts:
	gnu-system.am

gnu: inkscape: New module

* gnu/packages/inkscape.scm,
  gnu/packages/patches/inkscape-stray-comma.patch: New files.
* gnu-system.am (GNU_SYSTEM_MODULES): Add inkscape.scm.
  (dist_patch_DATA): Add inkscape-stray-comma.patch.

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