The ``sys.path[0]`` initialization change for bpo-29139 caused a regression
by revealing an inconsistency in how sys.path is initialized when executing
``__main__`` from a zipfile, directory, or other import location. The
interpreter now consistently avoids ever adding the import location's parent
directory to ``sys.path``, and ensures no other ``sys.path`` entries are
inadvertently modified when inserting the import location named on the
command line.
