Switch GKOP to using an MXBean so the pooled objects can be exposed without having to register each of the individually in JMX.
Remove the list of keys from the interface as a) the key class almost certainly won't be available to the JMX client and b) other attributes include key lists in their results.
Add a method to expose all the objects currently in the pool.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/pool/trunk@1507227 13f79535-47bb-0310-9956-ffa450edef68