bug#3462: Auto-fill VC log contents

[Lluis Vilanova <vilanova@ac.upc.edu>]

I've written a simple `log-edit-fill' command that automatically fills the
`VC-log' by means of `add-change-log-entry-other-window'
(`diff-add-change-log-entries-other-window', in fact, so improvements on that
come for free in `log-edit-fill').

Although the function is currently very tied to my needs, I think other people
can also benefit from it. I know, I can always push the diff info into the
Changelog file and after that import it into VC-log, but:

    1) `log-edit-fill' streamlines this process

    2) I do not keep Changelog files on my projects

For people who keep a Changelog file, I think it would be more comfortable to:

    1) Import all changes into the log message (I think that modifying
       `add-change-log-entry' and related functions to accept a destination
       buffer instead of a file would be valuable, so changes can be directly
       pushed into the `VC-log' buffer)

    2) On log pre-commit push the editions in the log message into the Changelog
       file, write it to disk and add to commit set.

Of course, the other way around is also possible: commiting from VC can open the
Changelog with newly added entries, then writing it (or a specific command)
triggers the extraction of newly written information into the log message.

Multiple options are available, all depends on the desired flow of actions.

Just hope it could be integrated into VC in a way that maintains my renegation
from Changelog files, so I can delete that snippet from my initialization files
:)

In any case, I hope it can save some typing to you.

Ah! The code...
    http://www.emacswiki.org/emacs/log-edit-fill

Read you,
     Lluis

PS: I've tested this code only in debian's emacs-snapshot

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