See #765, #761
Collections were relying on keeping in-memory list of all the objects
for any kind of operation which doesn't scale well the number of
objects in the database.
With this rewrite, objects are loaded only on demand which might
be pessimization in some edge cases but should improve performance
and memory footprint signifcantly.
Allow database to be initialized without opening, unify all the
open paths to retry on failure.
In API router make sure open requests are matched with acks in explicit
way.
This also enables re-open attempts in all the aptly commands, so it
should make running aptly CLI much easier now hopefully.
Fix up system tests for oldoldstable ;)
Andrey Smirnov
Chris Read