[Nix-dev] instructions for setting up apache + mediawiki is broken

[Marc Weber]

> - Is it not possible to have a default version?
If you do this you can break the system by updating it. For this reason
not having a default is the *only* way to protect against suprises.

> - If no default version, is there at least a way to print a *human
> readable* error message that hints the user about
Of course, provide patches. I introduced assertions long time ago.
Eg see b43.nix - so fix and provide a patch :)

Marc Weber