Avoid unnecessary rendertarget blitting in OpenGL light prepass mode.
Fixed too dark ambient lighting and environment cube mapping in OpenGL deferred mode.
Added new shader function GetQuadTexCoordNoFlip() which can be used to sample regular texture resources in postprocessing quad passes and documented it.
Removed Camera::SetFlipVertical() from the Lua script API as it should only be called internally to handle OpenGL / Direct3D9 differences.


git-svn-id: http://urho3d.googlecode.com/svn/trunk@2584 3bd170d8-ddcf-f82c-f583-7a401ccf5608