Since the original port of ES6 parser changes a few things have changed in the Graal.js parser. Most are refactorings and minor fixes.

In particular, we want to backport parts of the following changesets:

http://hg.openjdk.java.net/graal/graal-js-parser/rev/19d828ed3d80
http://hg.openjdk.java.net/graal/graal-js-parser/rev/ed2fa16c5bbd