scheduler.c:graph_has_edge: use isl_bool_not
scheduler.c:graph_has_edge: use isl_bool_not

When isl_bool was introduced in isl-0.14.1-479-g370a8b7d0 (introduce
isl_bool and isl_stat return types, Mon May 4 09:45:16 2015 +0200)
isl_bool_not was not yet available. It was only introduced in
isl-0.16.1-88-g9e2290e4 (add isl_bool_not, Tue Mar 1 17:15:59 2016
+0100), but at this point not all potential users were updated.

This is just a stylistic correction. The original code was correct.

Signed-off-by: Tobias Grosser <059b8b880f8441509ec8a65b50b4c6ae74ebea76@grosser.es>
Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

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