There are also overlay backbuffers, which aren't render targets. The
primarysurface and d3ddevice cap flags should be enough here.

If a format is not supported natively by opengl, a shader may be able
to convert it. Up to now, CheckDeviceFormat had magic knowldge which
GL extensions lead to which supported format. This patch adds
functions that allow CheckDeviceFormat to ask the actual
implementation for its capabilities.

When converting a makefile to a msvc .dsp file, if a line is ended with
a back slash, it will be joined with next line. This patch changes the
joining character from '\n' to a space in order to fix the bug of 
running MinGW32 on Windows.