Fix subtle typing issue in presence of recursion.
Fix subtle typing issue in presence of recursion.

pombredanne/pythran,pbrunet/pythran,artas360/pythran,pombredanne/pythran,pombredanne/pythran,pbrunet/pythran,hainm/pythran,pbrunet/pythran,hainm/pythran,artas360/pythran,hainm/pythran,artas360/pythran,serge-sans-paille/pythran,serge-sans-paille/pythran