[Checkers] checkers jar file and java 6

[Michael Ernst]

Mahmood-

Adam Warski says, regarding the new bundled checkers+javac jar file and
instructions:

> I tried, and it works great! :)
> One problem, though: works on java6; when using java5, I got a  
> "corrupted jar" error.
> 
> But now it's only one small step from creating a java web-start gui  
> demo :) Not to mention an ant task etc - the future is bright ;)

                    -Mike