Functions signal(), getsignal(), pthread_sigmask(), sigpending(),
sigwait() and valid_signals() were omitted.
If __all__ is not defined all non-builtin functions should have
correct __module__.
add private method to enum to support replacing global constants with Enum members:
- search for candidate constants via supplied filter
- create new enum class and members
- insert enum class and replace constants with members via supplied module name
- replace __reduce_ex__ with function that returns member name, so previous Python versions can unpickle
modify IntEnum classes to use new method
