We are not passing the same args to merge strategies when we are doing an
--interactive rebase as we do with a --merge rebase.  The merge strategy
should not need to be aware of which type of rebase is in effect.  Add a
testcase which checks for the appropriate args.
Signed-off-by: NElijah Newren <newren@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>