Added support for ``if __debug__:'' -- if -O is given, this form is recognized by the code generator and code generation for the test and the subsequent suite is suppressed. One must write *exactly* ``if __debug__:'' or ``elif __debug__:'' -- no parentheses or operators must be present, or the optimization is not carried through. Whitespace doesn't matter. Other uses of __debug__ will find __debug__ defined as 0 or 1 in the __builtin__ module.