[Checkers] new name for the Custom checker

[Michael Ernst]

> Mike and I recently discussed that "Custom checker" isn't a very good
> name, since the checker is by definition uncustomized. Can anyone
> think of a better name? So far, other possibilities include Simple
> checker, User checker, and Basic checker.

Another possibility (with its own disadvantages, like the others) is
Command Line Checker.

                    -Mike