Patch #1062033 / bug #1027771: clarify what happens when calling insertBefore() with refChild=None.
Patch #1062033 / bug #1027771: clarify what happens when calling
insertBefore() with refChild=None.

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