fix title to match original when relevant

We have found that some things like Grub inherit the environment
during the upgrade process, which turned its interface in french on
nutans.

This follows the principle of tutorial/reference/howto/discussion
distinction in documentation explained in:

https://www.divio.com/blog/documentation/

The "discussion" part being for now delegated to the issue
tracker (Trac). Eventually, each of those sections might be split in
their own pages.