[Checkers] Checkers tests

[Michael Ernst]

Directory annotations/checkers/tests has subdirectories
  flow
  custom
that do not seem to be used.  In particular, I can't find an Ant target
that runs these.  Could whoever is responsible for them either remove them
(possibly merging their functionality elsewhere) or else make it possible
(and preferably the default!) to run them?

                     Thanks,

                    -Mike