Add sortField attribute to datatable.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11788 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Fixed filtering bug, use correct expression

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11789 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c