git-p4: add failing test for name-rev rather than symbolic-ref

Using name-rev to find the current git branch means that git-p4
does not correctly get the current branch name if there are
multiple branches pointing at HEAD, or a tag.

This change adds a test case which demonstrates the problem.
Configuring which branches are allowed to be submitted from goes
wrong, as git-p4 gets confused about which branch is in use.

This appears to be the only place that git-p4 actually cares
about the current branch.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: luked99

t/t9807-git-p4-submit.sh

@@ -139,6 +139,22 @@ test_expect_success 'submit with master branch name from argv' '
 	)
 '
 
+test_expect_failure 'allow submit from branch with same revision but different name' '
+	test_when_finished cleanup_git &&
+	git p4 clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		test_commit "file8" &&
+		git checkout -b branch1 &&
+		git checkout -b branch2 &&
+		git config git-p4.skipSubmitEdit true &&
+		git config git-p4.allowSubmit "branch1" &&
+		test_must_fail git p4 submit &&
+		git checkout branch1 &&
+		git p4 submit
+	)
+'
+
 #
 # Basic submit tests, the five handled cases
 #