Various updates to the release checklist:

Various updates to the release checklist:
 - for 'ixion' read 'atreus' throughout
 - the signature-checking commands needed minor modifications to cope
   with more *sums files
 - stated a few things explicitly which were previously implied, in
   case the next inter-release gap is also long enough for me to
   forget them.

[originally from svn r9205]