Log Message:
Update wip/sxiv to sxiv-1.3.1.

pkgsrc changes:
 * Update the package to honor MASTER_SITES the a-la-github
 * Properly set -DVERSION in the CPPFLAGS in order to avoid gmake dependencies
   (via the SUBST framework)

Changes (1.3 and 1.3.1):
 * Various fixes and documentation improvements
 * Use thumbnails in EXIF tags
 * Added command to remove all image marks, bound to Ctrl-m