NodeCompilers refactoring

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C4635
DuckTyping functionality moved into PHP.Core.DuckTyping namespace

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C4636
Merge remote-tracking branch 'refs/remotes/tfs/default'