SF patch #443759: Add Interface to readline's add_history

SF patch #443759: Add Interface to readline's add_history

This was submitted by Moshe, but apparently he's too busy to check it
in himself.  He wrote:

    Here is a function in GNU readline called add_history,
    which is used to manage the history list. Though Python
    uses this function internally, it does not expose it to
    the Python programmer. This patch adds direct interface
    to this function with documentation.

    This could be used by friendly modules to "seed" the
    history with commands.