git-p4: document and test submit options

Clarify there is a -M option, but no -C.  These are both
configurable through variables.

Explain that the allowSubmit variable takes a comma-separated
list of branch names.

Catch earlier an invalid branch name given as an argument to
"git p4 clone".

Test option --origin, variable allowSubmit, and explicit master
branch name.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9807-git-p4-submit.sh

@@ -31,6 +31,60 @@ test_expect_success 'submit with no client dir' '
 	)
 '
 
+# make two commits, but tell it to apply only from HEAD^
+test_expect_success 'submit --origin' '
+	test_when_finished cleanup_git &&
+	"$GITP4" clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		test_commit "file3" &&
+		test_commit "file4" &&
+		git config git-p4.skipSubmitEdit true &&
+		"$GITP4" submit --origin=HEAD^
+	) &&
+	(
+		cd "$cli" &&
+		p4 sync &&
+		test_path_is_missing "file3.t" &&
+		test_path_is_file "file4.t"
+	)
+'
+
+test_expect_success 'submit with allowSubmit' '
+	test_when_finished cleanup_git &&
+	"$GITP4" clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		test_commit "file5" &&
+		git config git-p4.skipSubmitEdit true &&
+		git config git-p4.allowSubmit "nobranch" &&
+		test_must_fail "$GITP4" submit &&
+		git config git-p4.allowSubmit "nobranch,master" &&
+		"$GITP4" submit
+	)
+'
+
+test_expect_success 'submit with master branch name from argv' '
+	test_when_finished cleanup_git &&
+	"$GITP4" clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		test_commit "file6" &&
+		git config git-p4.skipSubmitEdit true &&
+		test_must_fail "$GITP4" submit nobranch &&
+		git branch otherbranch &&
+		git reset --hard HEAD^ &&
+		test_commit "file7" &&
+		"$GITP4" submit otherbranch
+	) &&
+	(
+		cd "$cli" &&
+		p4 sync &&
+		test_path_is_file "file6.t" &&
+		test_path_is_missing "file7.t"
+	)
+'
+
 test_expect_success 'kill p4d' '
 	kill_p4d
 '