Python specific `fill-column' enabled, lp:1037454

Customize new boolean `py-set-fill-column-p'. If `t', reads
`py-docstring-fill-column', default is 72
and `py-comment-fill-column, default is 79

Comment- and docstring settings might be disabled by
any non-integer value, which means: do not use a
different value of `fill-column' than emacs-wide