CTXUSAGE_CLEAR will apply the FBO state in a later patch.

Currently the ddraw capabilities were almost static, except of D3D
support. When overlay support is added, the caps depend on certain
settings in WineD3D or capabilities available from OpenGL and Xv. So
set those caps in wined3d as well.

Fixed function processing can only deal with values between 0 and 1
generally. Clamp the results of instructions that could produce bigger
or smaller values.