Fix dbconsole command for jdbcpostgresql adapter and JRuby

[antage]

dbconsole command doesn't recognize jdbcpostgresql adapter.
And JRuby requires some workaround to run psql in proper environment.

[jeremy]

Thanks for patching this, but it looks like a complex, brittle situation. It's probably better to wait to provide official support until it doesn't need such a complex workaround.