Email headers

[Dave Williss]

I was wondering how one would go about adding extra X-Bugzilla headers 
to BugMail.pm
It seems that the headers themselves come from data/params, (editable 
via web interface) but it refers to things like %component%, 
%reasonsheader%, etc.  I want a %priority%, but it doesn't seem to be set.

I can see where in BugMail.pm it sets members of a $substs hash with 
those values.
What I can't figure out is how to get the bug priority in that module so 
I can add a Priority header.

This is Bugzilla 2.22, BTW.