Pan Update

Here's the new snapshot.

• multi-parts are handled similarly to CVS version.
• new article test for multiple insertion of article, make sure refs only added once.
• new test for threading by subject.
• various related updates and bug fixes.
• partial update of db cleanup code.
• article doesn't store subject & author in memory anymore. They are loaded from db as needed. If this turns out to be to slow it's easily modified for ref counted strings or in-memory DB.
  

rev. 100