Implement a base delegator ot help maintenance of out of tree implemento...

...rs of Session

@emmanuelbernard, @sebersole, would you agree on adding something like this in ORM ?

It would greatly simplify the code of FullTextSessionImpl by isolating the simple delegate methods from those we actually need to override with specific logic.

Also, in case ORM changes some of the other 100 methods this would not affect Search compatibility.

Impact on Search would be as in:
https://github.com/Sanne/hibernate-search/commit/012cae2bd064925534b0849c98f9b70ff3f3d441
(proof of concept, but not working because of some classloading problem in AS7)