cherry-pick/revert -m: add tests

This adds a new test to check cherry-pick/revert of a merge
commit.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3502-cherry-pick-merge.sh

@@ -0,0 +1,123 @@
+#!/bin/sh
+
+test_description='cherry picking and reverting a merge
+
+		b---c
+	       /   /
+	initial---a
+
+'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+
+	>A &&
+	>B &&
+	git add A B &&
+	git commit -m "Initial" &&
+	git tag initial &&
+	git branch side &&
+	echo new line >A &&
+	git commit -m "add line to A" A &&
+	git tag a &&
+	git checkout side &&
+	echo new line >B &&
+	git commit -m "add line to B" B &&
+	git tag b &&
+	git checkout master &&
+	git merge side &&
+	git tag c
+
+'
+
+test_expect_success 'cherry-pick a non-merge with -m should fail' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	! git cherry-pick -m 1 b &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'cherry pick a merge without -m should fail' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	! git cherry-pick c &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'cherry pick a merge (1)' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	git cherry-pick -m 1 c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'cherry pick a merge (2)' '
+
+	git reset --hard &&
+	git checkout b^0 &&
+	git cherry-pick -m 2 c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'cherry pick a merge relative to nonexistent parent should fail' '
+
+	git reset --hard &&
+	git checkout b^0 &&
+	! git cherry-pick -m 3 c
+
+'
+
+test_expect_success 'revert a non-merge with -m should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert -m 1 b &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'revert a merge without -m should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'revert a merge (1)' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	git revert -m 1 c &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'revert a merge (2)' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	git revert -m 2 c &&
+	git diff --exit-code b
+
+'
+
+test_expect_success 'revert a merge relative to nonexistent parent should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert -m 3 c &&
+	git diff --exit-code c
+
+'
+
+test_done