lazutils: xpath: test for root and //

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@39914 4005530d-fff6-0310-9dd1-cebe43e6787f
lazutils: xpath: test for nodes

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@39915 4005530d-fff6-0310-9dd1-cebe43e6787f