My Windows 7 installation rejects mixing ps_3_0 with anything other than
vs_3_0 and vice versa, making testing how those versions pass varyings
moot. Since I have never seen an app mixing 3.0 and non-3.0 shaders I
see no reason to keep the tests.

winex11: Remember last window that had the XIC focus and use it in ToUnicode() to make dead keys work more reliably.

Calling surface_prepare_texture_internal() twice on the same surface is
harmless, but unnecessary.

Concept based on a patch by Stefan.