postgresql connect with specify db if 'postgres' does not work

Hi, 
here is my attempt to fix #675 
the thing is basicaly that we try to connect to 'postgres' db wich is a "protected" db... 
from local there is no trouble but from a remote location the postgres db is often no accessible...
so the install fail...

here i change small things to connect to the specified db if the postgres fail

:)