#449043 supporting __future__ in simulated shells
in support of PEP 264.
Much has changed from the patch version:
+ Repaired bad hex constant for nested_scopes.
+ Defined symbolic CO_xxx names so global search will find these uses.
+ Made the exported list of feature names explicit, instead of abusing
__all__ for this purpose (and redefined __all__ accordingly).
+ Added gross .compiler_flag verification to test___future__.py, and
reworked it a little to make use of the newly exported explicit list
of feature names.
Tim Peters