v4.1.1 — A store older than its own indexes

Fixed

• A store from an early version could not be opened at all, and there was no
  way out of it. Starting up creates the indexes, one of which is on a column
  that arrives with a migration scheduled to run after the engine is up. On a
  store old enough to predate that column, the index could not be created, so
  startup failed — and the migration that would have added the column could not
  run, because it runs after a startup that never finished. slm db migrate did
  not help either: it reports nothing failed and skips that class of migration by
  design. Any store in that state was stuck on the version it was already on.
  The column is now added before the index that needs it, so those stores open
  and finish upgrading on their own. Measured on a real 637 MB store: it went
  from refusing to start to a complete upgrade in 19 seconds, with all 7,707
  memories, 2,590 records and 848,945 connections unchanged and the integrity
  check clean.