This commit replaces the glDrawPixels and rectwrite_part with the very
nice (thanks zr!) glaDrawPixelsSafe() call. Result is:
- 3d window background image displays correctly onto the edges when
zoomed in extreme
- same for UV image window and sequence preview
- preview render now doesnt disappear when left part is outside window
(zr also deserves kick in butt for not doing this himself in NaN days!)
Especially from preview drawing quite some old hacks were deleted. It is
even quite some faster.
Please notify me when it doesnt work on your card... this now is just 100%
according opengl guidelines though :)
Also fixes bug #2100
341bb20dbd