Do not autosquash in case of an implied interactive rebase

The option to autosquash is only used in case of an interactive rebase.
When merges are preserved, rebase uses an interactive rebase internally,
but in this case autosquash should still be disabled.
Signed-off-by: NVincent van Ravesteijn <vfr@lyx.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -165,6 +165,7 @@ run_specific_rebase () {
 	if [ "$interactive_rebase" = implied ]; then
 		GIT_EDITOR=:
 		export GIT_EDITOR
+		autosquash=
 	fi
 	. git-rebase--$type
 }