Convert EffectorConcatenateTest from groovy to java

- So can actually debug properly in IDE, after
  test failed once in jenkins. Suspect there's
  a race in the test code...
Simplify EffectorConcatenateTest

- Use latches rather than notifyAll/wait, to avoid bugs on
  spurious wake-ups
- Simplify test to make it a lot easier to understand
Merge pull request #474 from aledsage/fix/EffectorConcatenateTest

Fix/effector concatenate test