This tells meld to resolve trivial conflicts before presenting the
user with the remaining conflicts.
This was attempted 5 years ago, but then --auto-merge was too new that
the patch was rejected out of concern that users still had an older
version of meld installed [1]. Maybe it's safe to assume that they
have a newer version now.
[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2013-April/050084.html