Older versions of meld listed --output in `meld --help`.
Newer versions only mention `meld [OPTIONS...]`.
Improve the checks to catch these newer versions.
Add a `mergetool.meld.hasOutput` configuration to allow
overriding the heuristic.
Reported-by: Andrey Novoseltsev <novoselt@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
David Aguilar