Forget the bound texture on fbo_create().

Just in case, since it overrides the texture.
Update native to cache bound fbos.
Only unbind the read fbo id draw can be skipped.
Avoid unbinding the draw fbo where possible.

If we're just going to bind another one, no need to trade around.
Rebind the fbo after inter-buffer copy.

Might be needed if the list is stalled, a copy is done, list unstalled,
and then something happens to flush a pending prim.
Perform intra-buffer blits directly.

As far as I can tell, this doesn't need a temp fbo.
Merge pull request #6800 from unknownbrackets/fbo-bind-opt

Optimize framebuffer binding and blits