Offline boostrap support

Hi from the Debian Haskell Packaging group!

In Debian, we'd like to ship Hoogle in such a way that it doesn't use online resources: the package should ship with enough data such that it's possible to generate the local databases "offline" (from bootstrap + local packages).

This used to work via some local hacks (see http://anonscm.debian.org/cgi-bin/darcsweb.cgi?r=pkg-haskell/haskell-hoogle;a=headblob;f=/files_hoogle/update-hoogle) until recently, but (if I read the changes correctly) issue #47 changed the way it looks for local data.

Fixing our script is doable, but I'm worried that things might break again, and silently (like this time; we only found that newer hoogle downloads data from the internet by accident), so I'm wondering what are your thoughts about improving hoogle's bootstrap mode?

A couple of potential improvements that come to mind:

• adding a flag "--no-download" which would make Hoogle abort if it can't find the required files
• documenting the list of files needed for bootstrap; the local install document doesn't say anything about this

Thanks in advance for your feedback!

Start by reviewing Hoogle's bootstrap mode and the local install documentation, then compare their handling of local data with the Debian script linked in the issue. Define whether the intended result is a no-download flag, documented bootstrap files, or both; done should prevent unexpected network access and make offline database generation reproducible.