If git-merge is invoked without a strategy argument it is probably
being run as a porcelain-ish command directly and is not being run
from within git-pull.  However we still should honor whatever merge
strategy the user may have selected in their configuration, just as
`git-pull .` would have.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>