SF bug #1105286:  Undocumented implicit strip() in split(None) string method
SF bug #1105286:  Undocumented implicit strip() in split(None) string method

Clarify the behavior when a string begins or ends with whitespace.

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