t3903: avoid applying onto dirty index

One of the tests in t3903 wants to make sure that applying a
stash that touches only "file" can still happen even if there
are working tree changes to "other-file". To do so, it adds
"other-file" to the index (since otherwise it is an
untracked file, voiding the purpose of the test).

But as we are about to refactor the dirty-index handling,
and as this test does not actually care about having a dirty
index (only a dirty working tree), let's bump the tracking
of "other-file" into the setup phase, so we can have _just_
a dirty working tree here.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3903-stash.sh

@@ -10,6 +10,8 @@ test_description='Test git stash'
 test_expect_success 'stash some dirty working directory' '
 	echo 1 > file &&
 	git add file &&
+	echo unrelated >other-file &&
+	git add other-file &&
 	test_tick &&
 	git commit -m initial &&
 	echo 2 > file &&
@@ -45,8 +47,6 @@ test_expect_success 'applying bogus stash does nothing' '
 
 test_expect_success 'apply does not need clean working directory' '
 	echo 4 >other-file &&
-	git add other-file &&
-	echo 5 >other-file &&
 	git stash apply &&
 	echo 3 >expect &&
 	test_cmp expect file