(coll) Create a single implementation of TreeMap instead of having two

In JDK6 and 7 there are two implementations of TreeMap: one in rt.jar and one in alt-rt.jar. The latter is considered more performant but contains behavioral incompatibilities. We should have a single performant implementation of TreeMap with the same behavior as the original implementation to avoid breaking applications. A submission of a new implementation whether internal or external should contain analysis of throughput versus memory footprint. A specjbb2005 benchmark can be used for such stress performance testing.