Merge in Anthony's new parser code, from the anthony-parser-branch:

Merge in Anthony's new parser code, from the anthony-parser-branch:

> ----------------------------
> revision 1.20.4.4
> date: 2003/06/12 09:14:17;  author: anthonybaxter;  state: Exp;  lines: +13 -6
> preamble is None when missing, not ''.
> Handle a couple of bogus formatted messages - now parses my main testsuite.
> Handle message/external-body.
> ----------------------------
> revision 1.20.4.3
> date: 2003/06/12 07:16:40;  author: anthonybaxter;  state: Exp;  lines: +6 -4
> epilogue-processing is now the same as the old parser - the newline at the
> end of the line with the --endboundary-- is included as part of the epilogue.
> Note that any whitespace after the boundary is _not_ part of the epilogue.
> ----------------------------
> revision 1.20.4.2
> date: 2003/06/12 06:39:09;  author: anthonybaxter;  state: Exp;  lines: +6 -4
> message/delivery-status fixed.
> HeaderParser fixed.
> ----------------------------
> revision 1.20.4.1
> date: 2003/06/12 06:08:56;  author: anthonybaxter;  state: Exp;  lines: +163 -129
> A work-in-progress snapshot of the new parser. A couple of known problems:
>
> - first (blank) line of MIME epilogues is being consumed
> - message/delivery-status isn't quite right
>
> It still needs a lot of cleanup, but right now it parses a whole lot of
> badness that the old parser failed on. I also need to think about adding
> back the old 'strict' flag in some way.
> =============================================================================