[Checkers] JSR-308 backward compatibility

[Michael Ernst]

Mahmood-

> Thanks for pointing this out.  I have added a statement about it

Thanks for writing this.  Your text looks pretty good; I made only minor
changes.

Remember:

  A feature does not exist if it is not documented.

So please make sure that documentation is a high priority.  Imperfect
documentation is much better than completely missing documentation!

                     Thanks,

                    -Mike