Add `indent-new-comment-line' and `reindent-then-newline-and-indent'
to the list of functions that we should be careful not to undo.
(refill-late-fill-paragraph-function): Remove.
(refill-saved-state): New var.
(refill-mode): Use it to save fill-paragraph-function.
Save also the value of auto-fill-function.
(refill-adjust-ignorable-overlay): New function.
(refill-pre-command-function): New function.
(refill-mode): Add `refill-pre-command-function' to `pre-command-hook'.
Initialize/cleanup `refill-ignorable-overlay'.
(refill-post-command-function): Don't reset refill-doit in the case
where a self-insertion command doesn't case a refill. Use
`refill-fill-paragraph-at', getting position from `refill-doit'.
(refill-after-change-function): Set `refill-doit' to END.
(refill-fill-paragraph-at): New function, mostly from old
refill-fill-paragraph. Use `refill-ignorable-overlay' to fill only the
paragraph's tail if possible. Update `refill-ignorable-overlay'. Don't
leave point inside the fill-prefix.
(refill-fill-paragraph): Use `refill-fill-paragraph-at'.
