Instead of parsing the DSN for each external libpq program we
are going to execute, provide a function that feeds them all
necessary parameters through the environment.
osm2pgsql is the first user.
The gazetteer output doesn't disable these functions when
writing to the place table but the triggers may contain
operations that cause misplanning for the query planner.
This replaces {data_dir}/settings throughout the code, so that
the configuration may be placed somewhere else in the directory
structure (e.g. in /etc).
With the website directory now tied to the project directory instead
of the build directory, it is no longer possible to use make for
running the web server.
Given that the module is now copied to the project directory
when no module path is set, we need the information that the
module path is empty. Therefore hand in the default module path
in a separate variable.
