Fix viewport when copying RGBA texture when IceT and EDL are used.

While pushing the RGBA texture to the framebuffer, the viewport was incorrect. In the screenshot below, both GL_TEXTURE0 and GL_COLOR_ATTACHMENT0 should be identical, but the viewport was set to be much larger than the actual framebuffer due to [ParaView magic].

This especially caused issues when compositing, as the depth buffer was pushed correctly and thus didn't match the color buffer:

This also adds the glInsertDebugMessage stuff (aka ANNOTATE_STREAMS) to a centralized location, vtkOpenGLRenderUtilities::MarkDebugEvent(const std::string&).