Truffle API Cleanup

[Christian Wimmer]

Hi all language developers,

The following changeset

 > Changeset: a12017c18d5d
> Author:    Christian Wimmer <christian.wimmer at oracle.com>
> Date:      2014-01-24 18:13 -0800
> URL:       http://hg.openjdk.java.net/graal/graal/rev/a12017c18d5d

contains some Truffle API changes: We reduced the visibility of classes 
and constructors that are not supposed to be used by language 
implementers. For example, Frame objects must always be created using 
the factory methods in the class Truffle, so the Default*Frame classes 
are now non-public.

The same hold for the class DefaultCallTarget. In order to have a public 
subclass of CallTarget that allows access to the RootNode that is 
called, we factored that part out into the new class RootCallTarget.

-Christian