use char instead of string

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@8873 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
New sorting impl.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@8874 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c