A few minor improvements for debugger client

I'm writing a freemarker debugger for Liferay IDE (Eclipse plugins) to debug freemarker templates executed inside of Liferay Portal Server.  See tickets here:
http://issues.liferay.com/browse/IDE-971
http://issues.liferay.com/browse/LPS-35774

During development of our debugger client we had to make several changes to get things to work for our Eclipse debugger.  I've pushed those changes to my fork and wanted to see if the freemarker project maintainers were interested in them.

-Added support for closing debug server socket
-Added support for shutting down debugger service
-Fixed bug with RemoteObject getting garbage collected
-Narrowed templateElement matching for breakpoints