Add additional test exposing bug #22.
Fix bug #22.

This code isn't very clear, but it is supposed to step back in the
token stream only if it has consumed an additional token past the end
of the arguments list. This always happens unless the parser has
reached the end of the token stream.
Fix incorrect value in test case.
#22: Copy and adapt test case to XPathHxTest. Also exposes bug #23.
Fix bug #23.
#22, #23: Fix silly code in test case.