Toggle Long Lines mode in this buffer.
With a prefix argument ARG, enable Long Lines mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.
When Long Lines mode is enabled, long lines are wrapped if they
extend beyond `fill-column'. The soft newlines used for line
wrapping will not show up when the text is yanked or saved to
disk.
If the variable `longlines-auto-wrap' is non-nil, lines are
automatically wrapped whenever the buffer is changed. You can
always call `fill-paragraph' to fill individual paragraphs.
If the variable `longlines-show-hard-newlines' is non-nil, hard
newlines are indicated with a symbol.
(fn &optional ARG)