Implemented core part of server side sorting for treetable.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10375 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
More work on treeTable sorting, added sortfunction and default sorting support.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10376 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Performance improvement

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10377 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c