gallium: fix some render to texture bugs

gallium: fix some render to texture bugs

Before, we were sometimes rendering into a stale texture because
st_finalize_texture() would discard the old texture and create a new one.

Moved st_update_framebuffer atom after texture validation so that we
can create a new renderbuffer surface if the texture changes.

Also, split texture validation into two parts: finalize_textures and
update_textures.  Do finalize_textures first to avoid getting into the
situtation where we're doing a pipe->surface_copy() mid-way through
state validation.

Some debug code still in place, but disabled...