Mechanism for handling GNU info's "dir" file

[jheiss]

GNU info uses a shared file /opt/tpkg/share/info/dir to provide a central index of all of the info documentation installed. We should document best practices for packages to handle updating that file when they are installed or removed.

This page looks to have some relevant documentation about how Debian handled this:

http://wiki.debian.org/Transitions/DpkgToGnuInstallInfo

Was: https://sourceforge.net/apps/trac/tpkg/ticket/37