HashTrieEngineTest: one-threaded compaction test was removed. Wait for the multi-threaded one!
HashTrieCompactingTest was added
HashTrieEngine.runCompaction(): now it's rather thread-safe. However, it can accidently eliminate some requests which were processed during compaction
HashTrieCompactingTest.stressTest(): now it waits for all compaction threads in the end
HashTrieIteratorModificationTest was added: it checks for correctness of iteration through collection which is being randomly modified (it is used in compaction)
HashTrieIterator:
  stores HashTrieEngine instead of HugeMappedFile now to avoid
  using old mapping after put() during iteration
HashTrieIterator.next(): now current leaf is checked for changes before return. If the leaf was removed, the next one is returned