MultiRangeMismatchTest: add old test back

Accidentally removed one test too many.
RangeTestHelperTest: cleanup imports
buildfile: add javadoc task
MultiRangeMismatchTest: javadoc comments
SingleAndMultiRangeNextTest: minor tweaks

- Added comments.
- Added javadoc links.
- Changed TestCase instantiation.
buildfile: correct doc path

The documentation was generated in the wrong directory.