AgentX, IPX: Restore default port (bug #3582283).

This reverts commit 7b9e03441c3dc3a07670ed01f5d04791a82c750c.
Add "-X" flag to prevent becoming a subagent
Default to None in all cases in value_to_pyobject

value_to_pyobject callers can't handle a NULL return, so
just default to returning None, and bump the refcount if
obj is still None when we're returning it.