Linux XShm capture plugin

  This plugin uses the MIT-SHM extension for the X-server to capture the
  desktop.

Todo:

 - handle resolution changes of screens
 - handle adding/removing screens while recording
 - support different depths

Contributing:

  If you are interested in helping out with the plugin, please drop by in the
  #obs-dev channel on quakenet.

References:
 - http://www.x.org/releases/current/doc/xextproto/shm.html