isl_map_coalesce: optionally bound the coefficients of wrapping constraints

isl_map_coalesce: optionally bound the coefficients of wrapping constraints

One of the methods for combining pairs of basic relations is based on wrapping.
The coefficients of these wrapping constraints may be much larger than
those of the constraints in the input.  If isl_map_coalesce is called
to simplify the representation of a relation, then constraints with
large coefficients are typically undesirable.  We therefore do not allow
the coefficients in the wrapping constraints to be larger than those
in the input, but we allow the user to override this choice.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>