"trait" instead of "trait class"

virtual -> open
 "final" introduced
 "wraps" dropped

idea/testData/codegen/classes/inheritance.jet

@@ -1,7 +1,7 @@
 // Changed when traits were introduced. May not make sense any more
 
 open class X(val x : Int) {}
-trait class Y {
+trait Y {
     abstract val y : Int
 }
 
@@ -11,7 +11,7 @@ class Point(x : Int, yy : Int) : X(x) , Y {
     override val y : Int = yy
 }
 
-trait class Abstract {}
+trait Abstract {}
 
 class P1(x : Int, yy : Y) : Abstract, X(x), Y by yy {}
 class P2(x : Int, yy : Y) : X(x), Abstract, Y by yy {}