add configuration variable for --autosquash option of interactive rebase

If you use this feature regularly you can now enable it by default. In
case the user wants to override this config on the commandline
--no-autosquash can be used to force disabling.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -111,6 +111,7 @@ VERBOSE=
 OK_TO_SKIP_PRE_REBASE=
 REBASE_ROOT=
 AUTOSQUASH=
+test "$(git config --bool rebase.autosquash)" = "true" && AUTOSQUASH=t
 NEVER_FF=
 
 GIT_CHERRY_PICK_HELP="  After resolving the conflicts,
@@ -795,6 +796,9 @@ first and then run 'git rebase --continue' again."
 	--autosquash)
 		AUTOSQUASH=t
 		;;
+	--no-autosquash)
+		AUTOSQUASH=
+		;;
 	--onto)
 		shift
 		ONTO=$(parse_onto "$1") ||