bug#35542: Installer does not display full backtrace on error

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

On Sat, May 04, 2019 at 11:43:28AM +0200, Mathieu Othacehe wrote:
> Hello,
> 
> > I believe I read about Guile error messages not doing line wrapping in
> > terminals on the Guix or Guile mailing lists recently, but I cannot
> > find it.  Proper line wrapping may be the better solution.
> 
> In fact the textbox where the backtrace is displayed isn't doing any
> line wrapping. The attached patch fixes the issue.
> 

I now get linewrapping, but provoked errors (these are not new bugs!)
are cut off like

In ./gnu/installer/keymap.scm
    163:7  8 (_ _)
In unknown file:
           7 (scm-error misc-error #f "~A" ("Unable to locate
keym…") …)

This seems like the same issue as Guile error backtraces only reaching
until the right end of the terminal and then getting cut off with
ellipses ….

I hope it is enough to guix pull from a Guix repo with the patch
applied and I do not get wrong output because I have not changed the
gnu/packages/package-management.scm Guix package to refer to a patched
version as well.

Regards,
Florian