Set to use new folder display and sync class defaults.

Accounts are now set:
Folder display mode = All except 2nd Class
Folder sync mode = Only 1st Class

Only the Inbox is set for:
Folder sync class = 1st Class
All other folders have class set to None for sync and display

Also restored an optimization on opening local folders that I
removed.  It is now optimistic, and in the normal case does not have
to make an explicit existence check