New home-page checker for ‘guix lint’

[Ludovic Courtès]

The ‘guix lint’ command now has a new ‘home-page’ checker that does what
you would expect:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix lint -c home-page 
gnu/packages/admin.scm:449:15: isc-dhcp-4.3.0: home page 
http://www.isc.org/products/DHCP/ not reachable: 404 ("Not Found")
gnu/packages/gtk.scm:391:14: gtk+-3.10.1: home page unreachable: No route to 
host
gnu/packages/image.scm:335:15: giblib-1.2.4: home page 
http://linuxbrit.co.uk/software/ not reachable: 500 ("Internal Server Error")
gnu/packages/make-bootstrap.scm:596:43: static-binaries-tarball-0: invalid 
value for home page
gnu/packages/stalonetray.scm:41:15: stalonetray-0.8.1: invalid home page URL: 
"stalonetray"
gnu/packages/xdisorg.scm:330:15: scrot-0.8: home page 
http://linuxbrit.co.uk/software/ not reachable: 500 ("Internal Server Error")
--8<---------------cut here---------------end--------------->8---

This has already allowed me to fix and update a bunch of URLs.

The impetus was a message by the gnu.org webmasters pointing to a list
of broken links on gnu.org, and
<https://www.gnu.org/software/guix/package-list.html> happened to have
many of them.

Comments and bug reports welcome!

Ludo’.