Better handling of bad user input.
Better handling of bad user input.

Raise a firendly error when the user does something stupid.

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