Make the add*() helper functions more robust for use after intialization is complete:  recompute _dirs_in_sys_path each time these functions are entered after module initialization is complete, and reset before returning to user code.
Make the add*() helper functions more robust for use after intialization
is complete:  recompute _dirs_in_sys_path each time these functions are
entered after module initialization is complete, and reset before
returning to user code.

This closes SF patch #442983.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator