OpenGL: fix our ubo workaround when blend_func_extended is missing
OpenGL: remove small optimization

This one was introduced to reduce the glBindTexture and glActiveTexture calls. But it was quite a bit of logic and only an improvment on uploading/creating a texture, which is done rarely.
VideoCommon: merge trivial parts of VertexManager::Flush
fix windows debug comile

This is broken because of revision ebbf1d392bc5a90b556d793c07b789e100f10615
VertexLoader: load scale factor as const, this will save some assembler instructions
VertexLoader: inline destionation buffer
VertexLoader: temp class for reader/writer