[Bf-codereview] VIEWER: Add toggle to determine correct glBlendFunc with regards to associated or unassociated alpha (issue 5176042)

[troy.sobotka at gmail.com]

Reviewers: bf-codereview_blender.org,



Please review this at http://codereview.appspot.com/5176042/

Affected files:
   M     release/datafiles/blenderbuttons
   M     release/scripts/startup/bl_ui/space_image.py
   M     source/blender/editors/include/UI_icons.h
   M     source/blender/editors/space_image/image_draw.c
   M     source/blender/makesdna/DNA_space_types.h
   M     source/blender/makesrna/intern/rna_space.c