#19 Installer - Check for database connectivity

[Keith Flanagan]

Performing a quick check to see whether the PostgreSQL database(s) specified can be connected to prior to the responder "kick" step might prevent searching through server-side stack traces for common problems, including:
* Database server not listening for TCP connections
* Database server not allowing TCP connections for particular users/databases
* Firewall blocking standard database ports
* Incorrect database username/passwords
* Incorrect database user permissions