Add proper error logging for an unlikely situation
Add proper error logging for an unlikely situation

The test suite did not capture the situation when an exception was
raised in Python and not in Pythran.

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