isl_map_coalesce: allow extensions to stick out by one
That is, allow the basic map that is about to be extended
to include the other one to also have some cut constraints,
as long as relaxing these cut constraints by one makes them valid.
The function is_adj_eq_extension has already been extended
to is_relaxed_extension to handle these cut constraints
in the previous commit.
This commit simply collects the cut constraints and
checks that relaxing them by one is sufficient.
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>