Problem reported by David Engster in:
http://lists.gnu.org/archive/html/emacs-devel/2016-03/msg01270.html
* admin/gitmerge.el (gitmerge-commit-message):
Truncate the computed commit message to at most 72 characters per line.
(gitmerge-maybe-resume): Don’t use "-" as the commit message for
merges; use the computed commit message instead.
This should avoid the problem we recently had with
automatically-generated merge messages, while still letting people
specify commits not to merge.
* admin/gitmerge.el (gitmerge-skip-regexp): Add "do not merge".
(gitmerge-highlight-skip-regexp): Fold case when searching
for gitmerge-skip-regexp.
* admin/gitmerge.el (gitmerge-missing): Use '--left-only' since we
only want commits from the branch that is to be merged.
(gitmerge-setup-log-buffer): Use the same symmetric range as in
`gitmerge-missing'.
* admin/gitmerge.el (gitmerge-default-branch): Change to
origin/emacs-25.
(gitmerge-missing): Use symmetric difference ('...') between
branch and master so that cherry-picks can be detected.
