Add missing TruffleBoundary.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/frame/FrameBuiltins.java

@@ -83,6 +83,7 @@ public Object clear(PFrame self, int idx) {
     @GenerateNodeFactory
     public abstract static class TruffleGetClassScopeNode extends PythonBuiltinNode {
         @Specialization
+        @TruffleBoundary
         public Object add(PFrame self) {
             // TODO: remove me
             // TODO: do it properly via the python API in super.__init__ :