* 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

Use != instead of <> since <> is documented as "obsolescent".
Use "is" and "is not" when comparing with None or type objects.

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?)