Pfff! I've written my best code after having one or two beers :)

Updates:
* Added class BytesWarning(Warning)
* Added -b/-bb command line args and Py_BytesWarningFlag
* issue PyErr_WarnEx(PyExc_BytesWarning) when Py_BytesWarningFlag is set.
* Added warning filter for BytesWarning that raises an exception if
Py_BytesWarningFlag > 1

Open questions:
* the warning filter isn't set when the initializer cannot load the
warning module (e.g. frozen apps). W/o the warning module Python is
screwed anyway and frozen apps would never add the -b argument.
* the warnings are only enabled with -b. They can't be enabled by
modifying the warnings.filters. Is this fine with you?