Fix error when no parenthesis in export statement
Fix error when no parenthesis in export statement

The previous, verbose code actually crashed when for example someone forgets to put parenthesis:

def test():
    ...

In that case the p token passed to p_error is None, and so it crashes when trying to access p.value

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