better fix to support nested components

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11099 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
[perf] reuse VisitContext

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11100 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Issue 6803:	p:columns does not support array of column definitions

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11101 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c