isl_qpolynomial_fold_set_dim_name: take into account object lives in map space
isl_qpolynomial_fold_set_dim_name: take into account object lives in map space

In particular, the space of the domain is different from
the space of the isl_qpolynomial_fold.
This was missing from isl-0.07-152-g3280c051ef (make isl_pw_* object live
in a map space, Tue Aug 30 16:47:59 2011 +0200).

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

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