If someone searches for a module that's on BackPAN but not CPAN, tell them

[neilb]

If someone searches for a module that's no longer on CPAN, but used to be, it would be neat if MetaCPAN could tell them that.

For example, if I search for Netscape::History it could say something like

No module Netscape::History on CPAN, but previously released as part of Netscape-History-3.01.tar.gz on BackPAN

[Grinnz]

This is sorta related to #1777 but it is true there are more reasons that a dist will not have any indexed version

[oalders]

This should be simple enough to do. We could just run an additional query if it looks like a module name but we get no matches. That should cover at least some cases.

[neilb]

Cool. I assume the additional query is on a BackPAN index, and if you find it is on BackPAN, the link shown could go to a page that explains what BackPAN is, and how to install something from BackPAN.

This came out of discussion with @jjatria on how to gracefully handle end-of-life of CPAN modules.

[oalders]

It'll be on the same ES type, but we'll search for status = 'backpan'.