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.
This is a exception to be thrown when the error occures because
of bad user data. We don't want to print a full stack trace in
these cases but just tell the user what went wrong.
The new functions always creates normal and partitioned functions.
Also adds specialised connection and cursor classes for adding
frequently used helper functions.
