Added support for pessimistic lock on retrieved entities to @QueryParam and @PostParam annotations

Example: @QueryParam("user", lock="WRITE")

Had to revert to providing support for EntityManager only, and not the more generic ObjectManager as before.
See https://groups.google.com/d/msg/doctrine-dev/pDS_tgvkVJM/OWn4FVBouzkJ for more information.