Proposition to make clusters have varying security for a given class

OK

Here it is. I have made two changes to handle access to a sub-set of a class' clusters.
This method is a patch, to give an idea of what can be done. I am not sure yet if that is the best solution (trapping the try/catch). There could be a method that does a soft check (ie not throwing exceptions when the rule is not found).

Also, for reviewers. I have done the iterator + count. Are there other places that would require a similar patch? And would it be better to move the fuction (duplicated) in a standard place. 

I wouldn't accept the patch AS-IS if I were you ;) But I think it is a very good basis for improved security. Multi-tenancy is something that I thought many users of orientdb were using already. When we have a final solution, I will write a little wiki page to give indications for future users.

ps. not sure about the iXXX naming convention. Is that for "input" parameters ?