Bug#1029665: Document APT::Clean-Installed on/true

[Dan Jacobson <jidanni@jidanni.org>]

Package: apt
Version: 2.5.5
Severity: minor
File: /usr/share/man/man8/apt-get.8.gz
X-Debbugs-No-Ack: noack

       autoclean (and the auto-clean alias since 1.1)
           Like clean, autoclean clears out the local repository of retrieved
           package files. The difference is that it only removes package files
           that can no longer be downloaded, and are largely useless. This
           allows a cache to be maintained over a long period without it
           growing out of control. The configuration option
           APT::Clean-Installed will prevent installed packages from being
           erased if it is set to off.

OK, but still you need to say what will happen if it is set to on.

Or is the default on? Etc.