This gets rid of the openHydraDB function and ensures that we
open the database in a consistent way.
Also drop the PostgreSQL sequence hacks. They don't seem to be
necessary anymore.
Because of the way DBIx::Class does prepared statements, even
innocuous queries such
$c->model('DB::Builds)->search({finished => 0})
can be extremely slow. This is because DBIx::Class prepares a
PostgreSQL statement
select ... from Builds where finished = ?
and since Builds is very large and there is a large fraction of rows
with "finished = 1", the PostgreSQL query planner decides to implement
this query with a sequential scan of the Builds table (despite the
existence of an index on "finished"), which is extremely slow. It
would be nice if we could tell DBIx::Class that constants should be
part of the prepared statement, i.e.
select ... from Builds where finished = 0
but AFAIK we can't.
