Op till now I've been using VERSION and DATE in replace.sed, but that
sometimes doesn't work well, e.g. if you're trying to process port
Makefiles. :-)

So after some experimenting with Python I came up with new identifiers;

   >>> print 'RFSVER'.encode('base64')
   UkZTVkVS

   >>> print 'RFSDAT'.encode('base64')
   UkZTREFU

These are very unlikely to be found in a text, and only contain upper- and
lowercase letters.
