SDL: Next stage cleanup, aligned texture conversion with current Windows/D3D code, and fixed overzealous GL texture caching. [R. Belmont]


nw: this fixes brightness/gamma/contrast on RGB32 format games (which has been broken since 2008, clearly a well-loved feature ;-) and breaks prescale.  Prescale will be fixed soon.
always a Clang (nw)
hd61830: added bitmap bounds checking, fixes nbmj8688 LCD games crash/assert (no whatsnew)