(prompt-for-change-log-name): Autoload this (for vc-comment-to-change-log).

(prompt-for-change-log-name): Autoload this (for vc-comment-to-change-log).
(add-change-log-entry): Take optional fourth arg NEW-ENTRY.  If non-nil,
never append to an existing entry.
(change-log-fill-paragraph): New function.
It might be nice to have a general feature to replace this.  The idea I
have is a variable giving a regexp matching text which should not be
moved from bol by filling.  change-log-mode would set this to "^\\s *\\s(".
But I don't feel up to implementing that today.
(change-log-mode-map): New defvar for keymap.  Bind M-q to
change-log-fill-paragraph in it.
(change-log-mode): Use that as local map.