Add 'make check-tutorial'.

Makefile

@@ -25,6 +25,9 @@ install::
 check:: build
 	$(RUNTEST) dulwich.tests.test_suite
 
+check-tutorial:: build
+	$(RUNTEST) dulwich.tests.tutorial_test_suite 
+
 check-nocompat:: build
 	$(RUNTEST) dulwich.tests.nocompat_test_suite