crypt32: Use CryptSIPRetrieveSubjectGuid to determine how to read a message object from a file, rather than assuming the source file is always a PE executable.

gdi32: Keep track of the number of unique fonts that are created and return this in the second DWORD of the GdiRealizationInfo structure.

This is mostly for correctness, in practice we should always be able
to avoid using CTXUSAGE_BLIT for offscreen targets when FBO ORM is
used.

Fixes some GL errors due to calling glDrawBuffer(GL_BACK) when an FBO
is still active.

As pointed out by Alexander Dorofeyev.