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.