* Removed func_hash and func_compare, so they can be treated as immutable
content-less objects (address hash and comparison)
* Added tests to that affect to test_funcattrs (also testing func_code
is writable)
* Reverse meaning of tests in test_opcodes which checked identical code
gets identical functions
with an instance of a derived class B would really raise an A, not a
B. Since Barry fixed this anomalous behaviour, I though I might as
well fix the test! (Hmm, Barry, did you not run the tests or did you
miss that test_opcodes failed?)