Add buffer option to datascroller to customize when to initiate a load for new chunk during scroll.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10514 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
cosmetics

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10515 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Better doc

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@10516 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c