- commit f6a5d002 inadvertently applied the "working copy" temporary file
  mechanism to both sqlite and xml document handling code paths, when it
  should only be used with sqlite files.  that, in turn, introduced a bug
  that causes XML files to not actually be processed at all if the
  --tmp-space option is turned on.  this patch fixes the problem, but also
  reorganizes the code to make the flow more linear, and hopefully easier
  to understand in the future.