Have an encrypted pgpass file

Hi,

Since .pgpass files contain plain-text passwords, I searched for an
alternative.
In the attached patch I've added the possibility to run a command to
produce the content of the pgpass file, in exactly the same format. In this
way I could use gpg or any other command to decrypt a pgpass file. It will
prefer the .pgpass file and will not call the command.

This would be my environment variable, to have no plain-text password:
PGPASSCOMMAND="gpg -q -d pgpass.gpg"

Other usages of the variable:
PGPASSCOMMAND="cat pgpass"
PGPASSCOMMAND="curl http://passwords/really-unsecure-pgpass"
PGPASSCOMMAND="my-own-secure-pgpass-script"

The submitted patch does it's job, though the command could throw errors.

What do you think of this solution?

Best regards,
Marco van Eck