add basic isl_union_map_intersect test
add basic isl_union_map_intersect test

This protects isl_union_map_intersect from completely breaking down and
provides a scaffolding for further tests of binary operations
on isl_union_map.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl