bug#61201: Installation hint crashes when user names contain at sign

["Ludovic Courtès" <ludovic.courtes@inria.fr>]

A funny thing was reported earlier today on the Café Guix channel:

--8<---------------cut here---------------start------------->8---
$ guix install hello  [17:52]
building profile with 5 packages...
hint: Backtrace:
          17 (primitive-load "/usr/local/bin/guix")
In guix/ui.scm:
   2279:7 16 (run-guix . )
  2242:10 15 (run-guix-command _ . )
In ice-9/boot-9.scm:
  1752:10 14 (with-exception-handler _ _ #:unwind? _ # )
In guix/status.scm:
    835:3 13 ()
    815:4 12 (call-with-status-report _ )
In guix/store.scm:
   1300:8 11 (call-with-build-handler _ )
   1300:8 10 (call-with-build-handler # ?)
In guix/build/syscalls.scm:
   1440:3  9 ()
   1407:4  8 (call-with-file-lock/no-wait _ _ )
In guix/scripts/package.scm:
    325:7  7 (build-and-use-profile _ "/var/guix/profiles/per-user/?" ?)
In guix/ui.scm:
    312:5  6 (display-hint _ )
  1451:24  5 (texi->plain-text )
In texinfo.scm:
  1132:22  4 (parse )
   980:31  3 (loop #<input: string 2b6e5926be70> (fragment) _ _ )
   967:36  2 (loop #<input: string 2b6e5926be70> #f # ?)
     92:2  1 (command-spec )
In ice-9/boot-9.scm:
  1685:16  0 (raise-exception _ #:continuable? )
 
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Throw to key #E1E1E1">parser-error' with args(#f "Unknown command" univ)'.
--8<---------------cut here---------------end--------------->8---

This is because the user name ends in “@univ…”, which ‘display-hint’
interprets as Texinfo.

Ludo’.