Replaces 'pself' with 'v_self' for uniformity

I forgot 'v_self' was already used elsewhere, I need to use the same
everywhere.
Minor fix to a test
Fixes calling methods with wrong arguments

Because of a missing error check, it called anyway and segfaulted. Also,
factored some more.
Begins the getattr logic, for JavaClass

Replaces the getmethod() method.