reduce queries for fetching many node`s data

As described in the cmf-mailing list (https://groups.google.com/forum/#!topic/symfony-cmf-devs/Bv3REKYwT80), this would be my first changes for reducing queries. There is still an test issue i will solve later.
How many node paths are there going to be? Some database backends have a limit on the number of elements you can have in an IN criteria IIRC