repeat testDataByLocaleOrdering with different save methods

- Factor out the save method into interface SaveMethod.
- Introduce testDataByLocaleOrderingFlushTus (identical to the old
  testDataByLocaleOrdering) and testDataByLocaleOrderingSaveMultiple.
- Add a code commenton clarifying why testDataByLocaleOrderingSaveMultiple
  works.
testBadLocale for BilingualTm

Obviously this test should fail early, but amazingly it all passes!  I added
an exception and structured it as an "expected fail" (which JUnit doesn't
realy have) to try to make this clear.
doc tweak
Merge pull request #7 from pimlott/master

More tests, a little doc.