[Checkers] Simplifying the checkers

[Michael Ernst]

I've spoken to each of you about this separately, but I should put it in
writing too and make sure that everything was clear.  I would like you to
push to incorporate the current framework features in your checkers, with
a strong preference for doing this before the release today.

Matt has mentioned that the interned checker can be made shorter and
clearer; I'm pretty sure that Telmo's Javari checker isn't using the latest
features; and I think even Mahmood said he hadn't finished incorporating
all of the latest features in the IGJ checker.

I would like to get this done soon, for several reasons:
 1. It should be really easy, especially if the framework is
    well-documented.  So we should get it out of the way.
 2. It will simplify writing new features and debugging existing checkers,
    so it should pay for itself.
 3. People will be writing their own checkers based primarily on looking at
    ours, and I want them to have good examples to work from.  On a related
    note, the Interned checker is reproduced in the manual, and I don't
    want to be embarrassed by it.

Let me know if there is any problem with this.

Thanks!

                    -Mike