wined3d: Implement support for gamma corrected (sRGB) texture loading

[Stefan Dösinger]

Appart of two things Henri already said the patch looks good to me(Use device 
in texture.c, break out the changes to surface_upload_data and 
surface_download data into seperate patches).

As for a wine test, I think its not easy to test it reliably since the opengl 
extension gives implementors quite a lot of room and doesn't require exact 
results. I think all we can reasonably test for are the oddnessnes hl2 
requires, like gamma-corrected Q8W8V8U8 and what the rendering outcome is - 
but that should go into a different patch.