t3508 (cherry-pick): futureproof against unmerged files

Each of the tests in t3508 begins by navigating to a sane state:

	git checkout master &&
	git reset --hard $commit

If a previous test left unmerged files around, they are untouched and
the checkout fails, causing later tests to fail, too.  This is not a
problem in practice because no test except the final one produces
unmerged files.

But as a futureproofing measure, it is still best to avoid the problem
with 'checkout -f'.  In particular, this is needed for new tests to be
added to the end of the script.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3508-cherry-pick-many-commits.sh

@@ -23,7 +23,7 @@ test_expect_success setup '
 '
 
 test_expect_success 'cherry-pick first..fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard first &&
 	test_tick &&
 	git cherry-pick first..fourth &&
@@ -33,7 +33,7 @@ test_expect_success 'cherry-pick first..fourth works' '
 '
 
 test_expect_success 'cherry-pick --ff first..fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard first &&
 	test_tick &&
 	git cherry-pick --ff first..fourth &&
@@ -43,7 +43,7 @@ test_expect_success 'cherry-pick --ff first..fourth works' '
 '
 
 test_expect_success 'cherry-pick -n first..fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard first &&
 	test_tick &&
 	git cherry-pick -n first..fourth &&
@@ -53,7 +53,7 @@ test_expect_success 'cherry-pick -n first..fourth works' '
 '
 
 test_expect_success 'revert first..fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard fourth &&
 	test_tick &&
 	git revert first..fourth &&
@@ -63,7 +63,7 @@ test_expect_success 'revert first..fourth works' '
 '
 
 test_expect_success 'revert ^first fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard fourth &&
 	test_tick &&
 	git revert ^first fourth &&
@@ -73,7 +73,7 @@ test_expect_success 'revert ^first fourth works' '
 '
 
 test_expect_success 'revert fourth fourth~1 fourth~2 works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard fourth &&
 	test_tick &&
 	git revert fourth fourth~1 fourth~2 &&
@@ -83,7 +83,7 @@ test_expect_success 'revert fourth fourth~1 fourth~2 works' '
 '
 
 test_expect_failure 'cherry-pick -3 fourth works' '
-	git checkout master &&
+	git checkout -f master &&
 	git reset --hard first &&
 	test_tick &&
 	git cherry-pick -3 fourth &&