Improved importLDIF code.


Importer.java:
Added ImportTask.dnIndexKey to avoid recreating this object.
In flushIndexBuffers(), call Future.get() on all the futures at the end of the method.
Removed unused ScratchFileWriterTask.tmpArray.
In clearIndexes(), added WriteableStorage parameter.
In setIndexesListsToBeRebuilt(), do not copy list unnecessarily.
Extracted method setTrusted(Collection<Index>, boolean trusted).
In processIndexes(), do not create a new IndexKey object, reuse the already existing one.
Added IndexKey.toString().

EntryContainer.java:
In clearDatabase(), added a WriteableStorage parameter + simplified the code thanks to this.