CopyOnWriteMap

I finally got around to writing an implementation of java.util.Map, which provides a fast, concurrent way to access a Map. Write operations are more expensive, but you would only want to use this class if reading is your primary objective. I had found a few other implementations of a copy-on-write Map, but I did not think they were quite right. With some help from the MINA team, I have the class in the trunk of MINA and all is well.