docs patch: dicts and sets

[Alan Isaac]

This is an attempt to synthesize Bill and Carsten's proposals.
(I'm changing the subject line to better match the topic.)

http://docs.python.org/lib/typesmapping.html: for footnote (3)

        Keys and values are listed in an arbitrary order.  This order is
        indeterminate and generally depends on factors outside the scope of
the
        containing program.  However, if items(), keys(), values(),
        iteritems(), iterkeys(), and itervalues() are called with no
        intervening modifications to the dictionary, the lists will directly
        correspond.

http://docs.python.org/lib/types-set.html: append a new sentence to 2nd par.

        Iteration over a set returns elements in an indeterminate
order,which
        generally depends on factors outside the scope of the containing
        program.

Alan Isaac