Use an 'appendstack.Accumulator' for profile's '_pending_alerts.

Avoiding conflicts, both with other web requests and with digest script.
Update digest processing to use 'Accumulator.consume' API.
More explicit test, better clarity.
Add evolve44 to convert profiles to use Accumulator for _pending_alerts.
Add evolve44 to convert profiles to use Accumulator for _pending_alerts.
Note change for this branch.
Release 3.107 with existing m125 changes.
Dev bump.
Merge tseaver-1122345-deconflict_profile_pending_alerts.