rebase: support --no-autostash

This is documented as an option but we don't actually accept it.
Support it so that it is possible to override the "rebase.autostash"
config variable.

Reported-by: Daniel Hahler <genml+git-2014@thequod.de>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -14,7 +14,7 @@ git-rebase --continue | --abort | --skip | --edit-todo
  Available options are
 v,verbose!         display a diffstat of what changed upstream
 q,quiet!           be quiet. implies --no-stat
-autostash!         automatically stash/stash pop before and after
+autostash          automatically stash/stash pop before and after
 fork-point         use 'merge-base --fork-point' to refine upstream
 onto=!             rebase onto given branch instead of upstream
 p,preserve-merges! try to recreate merges instead of ignoring them
@@ -292,6 +292,9 @@ do
 	--autostash)
 		autostash=true
 		;;
+	--no-autostash)
+		autostash=false
+		;;
 	--verbose)
 		verbose=t
 		diffstat=t

t/t3420-rebase-autostash.sh

@@ -37,6 +37,16 @@ testrebase() {
 	type=$1
 	dotest=$2
 
+	test_expect_success "rebase$type: dirty worktree, --no-autostash" '
+		test_config rebase.autostash true &&
+		git reset --hard &&
+		git checkout -b rebased-feature-branch feature-branch &&
+		test_when_finished git branch -D rebased-feature-branch &&
+		test_when_finished git checkout feature-branch &&
+		echo dirty >>file3 &&
+		test_must_fail git rebase$type --no-autostash unrelated-onto-branch
+	'
+
 	test_expect_success "rebase$type: dirty worktree, non-conflicting rebase" '
 		test_config rebase.autostash true &&
 		git reset --hard &&