Added copy() method to Query.php and made NestedSet.php use it because native clone() does not work. Also Added ->getSql() to getRootAlias() so that _aliasMap is present after the parsing.

- Removed the reserved alias "base" from the nested set. It's no longer necessary to use that. Use whatever alias you want.

Improvements and enhancements to the NestedSet (not BC! please have a look at draft/nestedset_changes.tree).
Added a model that was missing in the repos (model/BlogTag).
Updated a testcase.

Ticket: 328

--no commit message