While doing a big ol' rebuild, I was getting errors like this:

Starting download of /gnu/store/v55hic2g257hk2bc5bmr9abslf649pc0-fontconfig-2.11.94.tar.bz2
From http://www.freedesktop.org/software/fontconfig/release/fontconfig-2.11.94.tar.bz2...
following redirection to `https://www.freedesktop.org/software/fontconfig/release/fontconfig-2.11.94.tar.bz2'...
;;; Failed to autoload make-session in (gnutls):
;;; ERROR: missing interface for module (gnutls)
ERROR: In procedure module-lookup: Unbound variable: make-session
failed to download "/gnu/store/v55hic2g257hk2bc5bmr9abslf649pc0-fontconfig-2.11.94.tar.bz2" from "http://www.freedesktop.org/software/fontconfig/release/fontconfig-2.11.94.tar.bz2"
builder for `/gnu/store/mmbscw7df218xl0akmld7v8y3lx975fk-fontconfig-2.11.94.tar.bz2.drv' failed to produce output path `/gnu/store/v55hic2g257hk2bc5bmr9abslf649pc0-fontconfig-2.11.94.tar.bz2'

I suspect that hydra and other builders don't see this error because the
package is already in the store.  Apparently Guix only includes gnutls
as an input when the URL starts with https, so this sort of redirection
is not so great for Guix.  The attached patch updates all
freedesktop.org URLs to use https; apparently sourceforge too will need
the same treatment.

Andy