Update to 2.14

Changelog:

• Add --xinerama-index option for background setting (patch by James Knight)
• When removing the last image in slidsehow mode, stay on the last (previously second-to-last) image (patch by Lior Shiponi)
• Allow --sort and --randomize to override each other (most recently specified option wins) instead of always preferring --sort
• Thumbnail mode: Mark image as processed when executing an action (--action) by clicking on an image
• It is now possible to override feh's idea of the active xinerama screen using the --xinerama-index option
• Remove (undocumented) feature allowing to override feh's idea of the active xinerama screen by setting the XINERAMA_SCREEN environment variable