Refactored message sorting code by extracting the sort code from the sorted...

Refactored message sorting code by extracting the sort code from the sorted object (this was a bad design, worsened by the MessageProvider patch). Ideally, new Comparator classes should get promoted to top-level classes and not be enclosed in MessageList.
Subject stripper backported from issue258 branch (Utility.java)
The result is a cleaner MessageInfoHolder class.