A subtle issue with ifile-gnus

Problem:
After gnus-nnmail has decided which group(s) an article should go into
--- thus, therefore, after ifile has classified the article --- it
addes an Xref: header to the article body to indicate what group(s) it
got filed in.  Thus, when you train on incoming articles, you don't
see the Xref header.

When you re-file an article, however, the Xref header is present.  The
most common refiling action is to move something from non-spam to
spam.  

Thus, ifile rapidly learns that the presence of an Xref header is a
good indicator of spam.

This becomes a problem if you respool a bunch of mail for some reason
(e.g. you change your hand-written split rules and want to refile
accordingly) --- almost everything gets refiled into spam because of
the Xref header.

Solution:

The general form of the solution to this problem, under the assumption
that I can't really fix the gnus problem, is to cause ifile to ignore
Xref headers.  I don't want it to ignore other headers, since often
they really are good indicators of spam, though.  This leads to two
obvious options:

- put a wrapper script around ifile that filters out the Xref header
- give ifile a new flag to enable ignoring specified individual
  headers

I'm inclined toward the second option.  What do other people think?

Jeremy