RFC: Possibility to re-edit last commit message

[Jari Aalto]

It happens that when the message is committed, it wasn't quite the way
it supposed to be:

    * formatting
    * grammar
    * typos
    * missing information
    * something come up, that fot to be mentioned

In case of local branches (not checked out one), it would be nice if the
message could be re-edited

    bzr ci --re-edit

And that would bring up the editor just like last time. After exiting
the editor, that message would be updated (no files updated)

Jari