add test (closes HaxeFoundation/hxcpp/173)

tests/unit/src/unit/Test.hx

@@ -315,6 +315,7 @@ class Test #if swf_mark implements mt.Protect #end {
 		classes.push(new TestSpod(sys.db.Sqlite.open("db.db3")));
 		#end
 		TestIssues.addIssueClasses("src/unit/issues", "unit.issues");
+		TestIssues.addIssueClasses("src/unit/hxcpp_issues", "unit.hxcpp_issues");
 		var current = null;
 		#if (!fail_eager)
 		try

tests/unit/src/unit/hxcpp_issues/Issue173.hx

@@ -0,0 +1,16 @@
+package unit.hxcpp_issues;
+
+private class X1 implements Y1 {
+    public function new () {}
+}
+
+private interface Y1 extends Z1 {}
+
+private interface Z1 {}
+
+class Issue173 extends Test {
+	function test() {
+        var z:Z1 = new X1();
+        t(z != null);
+	}
+}