Review round 1.

 - removed unused methods
 - use jsr166y.ConcurrentLinkedDeque instead of Java7's
 - modified benchmark to not take into account thread start-up
 - divided DequeRecycler into a thread-safe ConcurrentDequeRecycler that uses
   an AtomicInteger to track its size and a NOT thread-safe DequeRecycler that
   just uses the .size() method
 - use Thread.getId instead of Thread.hashCode to compute the recycler to use
   in the concurrent recycler
 - use SOFT_CONCURRENT as a default for CacheRecycler too (in addition to
   PageCacheRecycler)