Allow programatic generation of Suite classes

[Yishai]

Add an annotation to the Suite class called SuiteMethod that would annotate
a method that returns a Class[] array. The Suite would then be built from
the two annotations, Suite.SuiteClasses plus any methods on the class (and
enforce that they be public, static, take no parameters and return a
Class[] array) that are annotated with Suite.SuiteMethod and build the
Suite as a combination of all of the Arrays returned. Multiple methods
return the same class, my preference would be to only run the class once.

An alternative would be to create a separate runner for a class has the
@SuiteMethod.

[dsaff]

Thanks for the idea. This is easy enough for user code to do without changes to JUnit, so I think we should de-prioritize.

[conneronx]

Way to kill something that would be super useful.