Drop database users prior to DROP/CREATE database.

This fixes an annoying issue where one tries to rebuild the database,
and it fails due to there being existing connections.

The one thing that is potentially scary about this implementation is
that it means it's now a lot easier to accidentally drop your
production database by running the wrong script; might be worth adding
a "--force" flag controlling this behavior or something.

Thanks to Nemanja Stanarevic and Neeraj Wahi for prototypes of this
implementation!  They did most of the work and testing for this.

tools/postgres-init-dev-db

@@ -49,6 +49,8 @@ else
 fi
 chmod go-rw ~/.pgpass
 
+"$(dirname "$0")/../scripts/setup/terminate-psql-sessions" "$USERNAME" "$DBNAME" "$DBNAME_BASE"
+
 psql -h localhost postgres "$USERNAME" <<EOF
 DROP DATABASE IF EXISTS $DBNAME;
 DROP DATABASE IF EXISTS $DBNAME_BASE;