This patch removes inheritence from PresburgerSpace in IntegerRelation and
instead makes it a member of these classes.
This is required for three reasons:
- It prevents implicit casting to PresburgerSpace.
- Not all functions of PresburgerSpace need to be exposed by the deriving classes.
- IntegerRelation and IntegerPolyhedron are defined in a PresburgerSpace. It makes more sense for the space to be a member instead of them inheriting from a space.
why this change?