oleaut32: Clean up IFontDisp::Invoke by using VariantChangeTypeEx to coerce the input parameter into the correct type.

Instead of blindly dirtifying the surface LoadTexture keeps track of
the color key that was used when creating the opengl texture and
reloads the surface if the color key has changed.

ntdll: Renamed the NTDLL_get/from_server_timeout functions since they don't deal only with timeouts.

Also get rid of the unused timeout field.

Make it an unsigned int to save some space on Win64, if we need to
transfer more than 4Gb over the server pipe something is seriously
wrong.

configure: Add a check for the DGifOpen function in the gif_lib.h header as the v4 of the file does define it, while v3 doesn't.