Previous alpha-overing on black for RGB display wasn't so much useful
for artists, changed in a way:
- Made RGBA display default for node editor backdrop and image editor,
so it'll be clear that image does have alpha channel
- RGB display will ignore alpha channel completely
Reshuffled buttons for RGBA/RGB so now the order is following:
RGBA | RGB | Alpha | Z
Still to come: startup.blend shall be altered to make RGBA default.