I'm trying to compare how new a file is with the header obtained
from Net::HTTP.head().  I use

   STRFTIME_FORMAT = "%a, %d %b %Y %H:%M:%S GMT"
   timestamp = DateTime.strptime(lastmod, STRFTIME_FORMAT)

But I can't compare this with the results of File.mtime, because one
is a DateTime, and one is a Time.  Time::strptime or Time::strftime
don't exist.  Time#strftime does, but I can't pass a string to be
turned into a time into it.  Parsedate deosn't seem to handle this
case, either in so far as it has no str[fp]time.

Is there a cunning way to do this I have missed?  Do I need another
library and if so, what?

         Thank you,
         Hugh