'Add a path item to ``.entries``, finding any distributions on it
``find_distributions(entry, True)`` is used to find distributions
corresponding to the path entry, and they are added.  `entry` is
always appended to ``.entries``, even if it is already present.
(This is because ``sys.path`` can contain the same value more than
once, and the ``.entries`` of the ``sys.path`` WorkingSet should always
equal ``sys.path``.)'

def add_entry(self, entry):

    self.entry_keys.setdefault(entry, [])
    self.entries.append(entry)
    for dist in find_distributions(entry, True):
        self.add(dist, entry, False)
