[whisker] Switch to JUnit4 ...?

[Robert Burrell Donkin]

I'm comfortable with both junit3 and junit4, but perhaps other people 
might have a preference for one or the other. As I work on the 
documentation, I'm going to improve the test coverage as I go (and fix 
any issues discovered).

ATM Whisker uses JUnit3 but I'd be happy to update these tests to JUnit4 
now if that's easier for people.

Opinions?

Robert