[Mailman-Developers] Update MM 2.1.2->2.1.5 fails and no help from mailman-users

[Terri Oda]

If I recall correctly, Mailman still doesn't always deal gracefully 
with old pending stuff, so you may have to clear out those files before 
doing the upgrade (as well as upgrade python, as was already 
mentioned).

This used to be mentioned in the README or INSTALL files, and I'd 
assume it's still buried in there somewhere, although it's hard to 
blame you for missing it.