Bug#305142: CAN-2005-2214: insegure apt-setup

[Petter Reinholdtsen <pere@hungry.com>]

[Joey Hess]
> The only real solution to this bug is to remove support for
> passwords in the proxy setting. Making the file mode 600 by default,
> or even only if a password is present cripples the system for
> regular users by breaking apt-get source and hardly makes it anymore
> secure anyway.

An option is to only support the http_proxy and ftp_proxy environment
variables, but this is painful in other ways (bug #123144).

Another option is to move the proxy settings to a separate file and
read this file too.