ps 1.x supports only 8 constants, so the shader load code dirtifies the
first 8 on a shader switch. However, the constant load code reloaded all dirty
consts with clamping. That potentially left constants > 8 clamped.

winex11.drv: Fallback to X11DRV_SHM_NONE in X11DRV_DIB_DoCopyDIBSection() if dest doesn't match the pixmap.

Falling back to X11DRV_SHM_IMAGE doesn't work, the image's data isn't in
shared memory if the pixmap was created as Shm pixmap.

Also update the comments.

Based on a patch by Aric Stewart.

The header is wrong. There is simply no API to set this. The MS header does
not have this declaration either.

Most of this is "Copyright 2004 Huw Davies for CodeWeavers", I just did a
little bit of integration.