wined3d: Rewrite surface_modify_location() on top of surface_validate_location() and surface_invalidate_location().

Otherwise invoking winegcc on any platform where our first guess at
the link options fails results in a lot of confusing error messages.

This stops the tested gcc command from issuing a warning on Solaris.

It's not worth printing a FIXME for every VARTYPE we don't happen to
list in the switch statement.

Sizes of textures and stand-alone surfaces must be multiples of the
format's block size for DXTN formats. Since we create a texture for
everything (except in ddraw), this check also takes care of stand-alone
surfaces.

user32/tests: Test to show that SendMessage/PostMessage don't force caller activation context on window thread.