twisted.python.modules.OPTIMIZED_MODE is wrong with python -O

[ivank]

twisted.python.modules.OPTIMIZED_MODE is correct for python -OO, but not python -O:

It should be looking for not __debug__, instead of __doc__ is None (which is only correct for the python -OO case).

Python code in CPython uses __debug__ to determine whether .pyo files are relevant, so this method might be okay.