Some drivers apparently need private constants, or don't have an efficient
immval packing. For example, MacOS seems to need 1 float for each different
relative addressing offset. fglrx has the same issue, although it is more
efficient in general

Previously this worked on most drivers because the 16 + 4 reserved int and
bool constants kept the problem hidden. Now that we are more aggressive with
uniforms we have to keep free room for some drivers.

This allows better defining of driver desc fixups without adding extra if
lines for each card.

For starters, there's a fixup for the advertised GLSL constants in ATI cards.
fglrx advertises 512 GLSL uniforms instead of the supported 1024(means 128
instead of 256 vec4's). This bug was confirmed by ATI.

It's much easier to free it on release.

guidInstance should be the same from both places.

Fixing regression produced by "comctl32: Correct handling of toolbar
separators size". As it came out, some applications DO rely on iBitmap
value, but it can be received not with TB_GETBUTTONINFO, but with
TB_GETBITMAP.