bug#21829: guix import hackage failures

[Ludovic Courtès]

Paul van der Walt <address@hidden> skribis:

>  137: 4 [guix-import-hackage "xmonad-contrib"]
> In ice-9/format.scm:
> 1593: 3 [format #<output: file /dev/pts/1> ...]
>  766: 2 [format:format-work "~:[~*~;guix ~a: ~]~afailed to download cabal 
> file for package '~a'~%" ...]
>  200: 1 [tilde-dispatch]
> In unknown file:
>    ?: 0 [scm-error misc-error #f "~A" ("error in format") #f]

Commit 5453de3 fixes the easy part.  :-)

Strangely, ‘define-diagnostic’ in (guix ui) was defined so that we can
get ‘format’ warnings, but the trick doesn’t work outside of (guix ui)
itself.

Thanks,
Ludo’.