Switch source to use the new location at gnu.org.
This includes a tarball format change (tar.bz2 -> tar.xz),
something that wasn't possible on our Drupal Site installation.
Implicit: there's also a hash change.

Thanks to the team at GNU that handled this, although the
procedure took quiet a long time to finish.
-- 
GnuPG: A88C8ADD129828D7EAC02E52E22F9BBFEE348588
GnuPG: https://c.n0.is/ng0_pubkeys/tree/keys
  WWW: https://n0.is