alpha rename type parameters in generated anon default constructor

javac should alpha rename the generated type parameters in a generic
generated anonymous default constructor's type. This will allow the
following code in Enter

372 public void visitTypeParameter(TypeParameter tree) {
373 TypeVar a = (tree.type != null)
374 ? (TypeVar)tree.type
375 : new TypeVar(tree.name, env.info.scope.owner);
376 tree.type = a;

to be rewritten

373 TypeVar a = new TypeVar(tree.name, env.info.scope.owner);

And will leave the type variable symbols with correct owners.