Create serializable copy of synchronization strategy set.

Objects returned from managed methods should be serializable so they can be used via JMX remotely.

The key set of a HashMap is not serializable so a copy should be created.

The error that currently occurs when accessing the "synchronizationStrategies" attribute is:

```
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
	at com.sun.proxy.$Proxy0.getsynchronizationStrategies(Unknown Source)
	at HajdbcList.main(HajdbcList.java:40)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.rmi.UnmarshalException: error unmarshalling return; nested exception is: 
	java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: java.util.HashMap$KeySet
	at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:191)
	at com.sun.jmx.remote.internal.PRef.invoke(Unknown Source)
	at javax.management.remote.rmi.RMIConnectionImpl_Stub.getAttribute(Unknown Source)
	at javax.management.remote.rmi.RMIConnector$RemoteMBeanServerConnection.getAttribute(RMIConnector.java:901)
	at javax.management.MBeanServerInvocationHandler.invoke(MBeanServerInvocationHandler.java:280)
	... 7 more
Caused by: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: java.util.HashMap$KeySet
	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
	at sun.rmi.server.UnicastRef.unmarshalValue(UnicastRef.java:324)
	at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:173)
	... 11 more
Caused by: java.io.NotSerializableException: java.util.HashMap$KeySet
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
	at sun.rmi.server.UnicastRef.marshalValue(UnicastRef.java:292)
	at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:332)
	at sun.rmi.transport.Transport$1.run(Transport.java:177)
	at sun.rmi.transport.Transport$1.run(Transport.java:174)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
	at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:722)
```