XPath handling: several performance improvements, cache results of XPathElement#split

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2969 d35d4baa-7912-0410-b0ae-edacad209e15
FxContent: fixed an issue when reverting changes that were not present in the original content

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2970 d35d4baa-7912-0410-b0ae-edacad209e15
phrase engine: direct/indirect tree mapping

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2971 d35d4baa-7912-0410-b0ae-edacad209e15