Fixes #5779 with new PSPScreenShotDiag class
Only set depth update flag when depth write is enabled
Switch to a slider for alternative speed, and make its range 5-600%.
Allow the speed to go as low as 0% (at which point it becomes unlimited, since zero FPS limit in the code means unthrottle).
Update native
Oops, the vertexdecoder should read vertex alpha.

Copy/paste mistake... ugh.
Don't forget tex alpha if only a mip has none.

Mip levels should only move toward unknown.
Avoid the GE debugger affecting vertexFullAlpha.
Use an unsigned compare for x86 vertexalpha check.
Alt speed slider: Remove the rounding, since native does it automatically. Don't use an integer divide.