Fixes #715 IDE warning cast in generated crosslink methods

I added the base class as a second param in the phpdoc. I did this because when I changed the typehint of the passed parameter to be our base class then the IDE has thrown another warning (see picture). I couldn't find any clear method to get the base class so I created a new method in AbstracOMBuilder. If there is a better way please let me know.

![warning](https://cloud.githubusercontent.com/assets/884833/5382167/352d751e-80a8-11e4-89d0-63064ed2629d.jpg)