t3404: begin "exchange commits with -p" test with correct preconditions

The test case shows a bug in 'rebase -p', but even if the bug were fixed the test would fail because it did not ensure that the preconditions match the postconditions that were checked. Insert the suitable 'git checkout'.

---
Could it be that this bug existed since the test case was introduced in cddb42d2?

(The bug in git-rebase has not been fixed since then, unfortunately.)

-- Hannes

 t/t3404-rebase-interactive.sh | 1 +
 1 file changed, 1 insertion(+)

index 4983bd7..025c1c6 100755
@@ -247,6 +247,7 @@ test_expect_success '-p handles "no changes" gracefully' '
 '
 
 test_expect_failure 'exchange two commits with -p' '
+	git checkout H &&
 	FAKE_LINES="2 1" git rebase -i -p HEAD~2 &&
 	test H = $(git cat-file commit HEAD^ | sed -ne \$p) &&
 	test G = $(git cat-file commit HEAD | sed -ne \$p)

1.7.10.2.529.g0c18cfd

Yeah, looks like it was always broken. I remember sanity checking by removing the "-p", too, but that was probably before moving the test to join the other -p tests. Thanks for fixing it.