python - be: Throw IndexError when subscript is out of bounds.

Log Message:
-----------
Throw IndexError when subscript is out of bounds.

Not doing this in subscript caused the default iterator to return None
forever--well, until MemoryError got raised.

Modified Files:
--------------
be/src/type:
array.c (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/type/array.c.diff?r1=1.6&r2=1.7)