Tensor products, quotients, etc., of free modules

Comment from Mike: I'm highly interested in this functionality as I need it for a lot of things. It would be nice to be able to tensor over rings other than just the base ring.

Soroosh's Wish List: Here is a list of things that I think it would be nice to have in Sage. I think some of them are in already.

Comment from Justin:

As of Monday, we have some code running. It's barely a beginning. How this fits into the class hierarchy is not yet clear. Comments welcome ([email protected], [email protected]).