Make sure git-stash works from subdirectory.

We say "SUBDIRECTORY_OK" but we did not chdir to toplevel; this
is fine as long as everything we use can be started from a
subdirectory, but unfortunately "merge-recursive" is not one of
the programs you can safely use from a subdirectory.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-stash.sh

@@ -6,6 +6,7 @@ USAGE='[ | list | show | apply | clear]'
 SUBDIRECTORY_OK=Yes
 . git-sh-setup
 require_work_tree
+cd_to_toplevel
 
 TMP="$GIT_DIR/.git-stash.$$"
 trap 'rm -f "$TMP-*"' 0

t/t3903-stash.sh

@@ -66,4 +66,11 @@ test_expect_success 'apply stashed changes (including index)' '
 	test 1 = $(git show HEAD:file)
 '
 
+test_expect_success 'unstashing in a subdirectory' '
+	git reset --hard HEAD &&
+	mkdir subdir &&
+	cd subdir &&
+	git stash apply
+'
+
 test_done