Blender Git Loki

minor cleanup, minimal functional change.
replace some long duplicated, ifdef'd if statements for image extension.
- new function: BLI_testextensie_array(), can take an array of extensions.
- define extension arrays: imb_ext_image, imb_ext_movie, imb_ext_sound - we could have more of these.
- removed amiga extensions iff and lbm