[development] access control APIs

[Metzler, David]

I've been working up a patch to submit for simple_access.  Basically,
I'm trying to achieve the concept of letting a student say "only share
this node with the faculty ", but of course the students aren't and
shouuldn't  in the faculty role.  

I'm sort of stuck.  

I had no problem modifying simple_access to display all the groups, but
reading the API documentation, I'm unclear as to whether there's a hook
that will let me override the permissions behavior defined in the
node_access table.

If I read correctly hook_access only applies to nodes that I define in
my module, but I was looking for site wide behavior.   

Can hook_node_grants be leveraged to do this?  It's a little unclear to
me from the docs. Is there a different recommended strategy? 

Dave