Check for custom made xbmc version in rescan 

Service rescan only starts it's backend program, if the version shipping with RetroRig is currently installed. This way user can install a regular version of XBMC, and rescan doesn't kills it upon switch on the controller.

Please refer to the test protocol: http://slexy.org/view/s20vAgsSIM

To get this commit working smootly, you must first update xbmc-bin_Gotham_V13.1_patched_for_RetroRig.deb (according to the latest build instructions from build-xbmc.sh) and have it updated on libregeek.