Filter out DeprecationWarnings in test suite, so 'python -3' works

The test suite passes with python version 2 & 3, but fails with 'python -3' due to a DeprecationWarning, which is a little surprising. This filters out DeprecationWarning so the test suite also passes when run with 'python -3'.

It should probably check for sys.py3kwarning to be completey correct.