This fixes <https://bugs.freedesktop.org/show_bug.cgi?id=104325> which showed
up in Guix as an infinite loop during cairocffi tests.
* gnu/packages/patches/cairo-setjmp-wrapper.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/gtk.scm (cairo)[source](patches): Add it.
* gnu/packages/gimp.scm (babl)[source]: Use HTTPS for ftp.gtk.org.
* gnu/packages/gnome.scm (rest)[home-page]: Use HTTPS for www.gtk.org.
* gnu/packages/gtk.scm (gtk+-2, gtk-doc)[home-page]: Likewise.
The venerable search.cpan.org has retired[0].
[0]: https://log.perl.org/2018/05/goodbye-search-dot-cpan-dot-org.html
* guix/import/cpan.scm (cpan-home): Generate metacpan.org home page URIs.
Update all previously generated ones in (gnu packages) to their
canonical new homes.
* gnu/packages/gtk.scm (gtk-doc)[source]: Update to 1.27.
[arguments]<#:phases>[patch-gtk-doc-scan]: New phase.
[arguments]<#:phases>[patch-test-out]: New phase.
[propagated-inputs]: Add python-six.