add __getitem__ method to PyBase object
add __getitem__ method to PyBase object

This allow us to test the properties of the nodes, and is also more
symmetrical with the __setitem__ method.

prechelt/pyth,prechelt/pyth,sheepeatingtaz/pyth,pombredanne/pyth,kippr/pyth,brendonh/pyth,kippr/pyth,eriol/pyth