Still some open questions.. and at any rate, no additional piglit passes
due to various wrap modes that we need to emulate in at least some
cases :-(

But it does fix some mystery page-faults.. So add some comments in the
code where there are things that we need to emulate or do more r/e, and
push as-is.

Signed-off-by: Rob Clark <robclark@freedesktop.org>