[MlMt] Counters preference not being remembered.

[Scott A. McIntyre]

Hi,

In Version 1.8 (4447), I've adjusted the counters that are displayed on 
the dock but the changes are not remembered across restarts of the 
application.

If it matters, one of the counters refers to Unread in a Smart Mailbox; 
but that may not be a factor.

100% repeatable here on this 10.10b6 Yosemite box (yes, know I'm running 
alpha on beta...).

Scott