Add docs and onerror callback

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9564 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Fixed #5569

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9565 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c