bug#60936: 30.0.50; ERC >5.5: Add erc-fill style based on visual-line-mode

[J.P.]

tzakmagiel writes:

> +1'ing this the issue in Message #166 for visibility. I raised this question
> under the nick "alcor" on #erc yesterday, and I agree that the default
> behavior of `fill-wrap' (i.e. without `scrolltobottom') might be
> confusing/unexpected for new `fill-wrap' users (such as myself, in this case).
>
> For the record, the behavior without the scrolltobottom module could be
> described as "messages tend to drift upward on screen, gradually increasing
> the whitespace between prompt and bottom of window" (This description courtesy
> of corwin on #erc).
>
>>I'm thinking it might make sense to have `fill-wrap' formally depend on
> `scrolltobottom', even though there's no technical reason to do so.
>
> +1 on that too. The behavior with `scrolltobottom' makes more sense (as a
> default) and is more in line with other IRC clients, where the message prompt
> is kept at the bottom of the window.

Appreciate the input. `fill-wrap' now activates `scrolltobottom' if not
already enabled and also reminds users to add it to `erc-modules' when
that's the case:

  https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=9668b4f9

Please let us know if something's still amiss or if the fix is otherwise
inadequate. Thanks.