Fixes for Python/C++ implementation in open-source:

  * Rosy hack doesn't apply (that test should be removed
    for the open-source release).

  * Added our own copy of parameterized.py (the open-source
    version of Google Apputils doesn't contain it).

  * The C++ Descriptor object didn't implement extension_ranges.

  * Had to implement a hack around returning EncodeError, to
    work around the module-loading behavior of the test runner.