add more tests

Author: liufengyun

tests/pos/i2051.scala

@@ -1,2 +1,9 @@
 class A[T](val x:T)
 class B[T](override val x:T) extends A[T](x)
+
+class C[T](val x:T, val y: Int, val z: Boolean)
+class D[T](override val x:T, y: Int, z: Boolean) extends C[T](x, y, z)
+
+trait X(val x: Int, y: Int, z: Int)
+trait Y(override val x: Int, y: Int, z: Int) extends X
+class Z(override val x: Int, y: Int, z: Int) extends Y(x, y, z) with X(x, y, z)