I've updated my patch to work with the changes introduced to libpq by allowing multiple hosts.
On Fabien's recommendations, I've kept the variable dot_pgpassfile_used, however I renamed that to pgpassfile_used, to keep a consistent naming scheme.
I'm still not sure about the amount of error messages produced by libpq, I think it would be ideal to report an error while accessing a file provided in the connection string, however I would not report that same type of error when the .pgpass file has been tried to retrieve a password.
(Else, you'd get an error message on every connection string that doesn't specify a pgpassfile or password, since .pgpass will be checked every time, before prompting the user to input the password)
regards,
Julian Markwort