Update vsync on resize, and before first FBO

May take care of #4440.  Per #6182, vsync is only broken when the post shader was previously enabled, but not if it is enabled while in game.  This implies it has to do with the order of operations.

The only logical thing is that we are creating an FBO before setting it, and this matters somehow.  These changes set vsync slightly more liberally in attempt to kill the problem.

I have not noticed the problem myself, so I can't test.

-[Unknown]