[WIP] Node cloning

Add ability to clone a node from one workspace into another.

Work in progress, related pull requests in jackalope, jackalope-jackrabbit, phpcr-api-tests

See:
 * https://groups.google.com/forum/?fromgroups=#!topic/symfony-cmf-devs/SZgcc7hpKxg 
 * http://www.day.com/specs/jcr/2.0/10_Writing.html#10.8%20Cloning%20and%20Updating%20Nodes