git-merge: add support for branch.<name>.mergeoptions
This enables per branch configuration of merge options. Currently, the most
useful options to specify per branch are --squash, --summary/--no-summary
and possibly --strategy, but all options are supported.
Note: Options containing whitespace will _not_ be handled correctly. Luckily,
the only option which can include whitespace is --message and it doesn't
make much sense to give that option a default value.
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>