Reduce object allocations

While doing some performance analysis we have found that we can reduce object allocations a number of places in the code base.

• In JDBCStoreManager we can create a simple pool(list) of CancelPreparedStatement/CancelStatement.
• BrokerImpl.initializeOperatingSet, use a java.util.IdentityHashMap rather than org.apache.commons.collections.map.IdentityMap.IdentityMap.