git-merge: make recursive the default strategy

git-merge: make recursive the default strategy

git-pull invoked merge with recursive as the default strategy
for some time now; match it in the git-merge itself.  Also avoid
listing more than one strategy on default because we have only
one strategy that can resolve an octopus and we are already
counting heads here.  This reduces the need to stash away local
modifications.

Signed-off-by: Junio C Hamano <junkio@cox.net>