Add diffs parameter to bugmail_recipients hook. r=mkanat.

Bugzilla/BugMail.pm

@@ -191,7 +191,7 @@ sub Send {
     
     Bugzilla::Hook::process('bugmail_recipients',
                             { bug => $bug, recipients => \%recipients,
-                              users => \%user_cache });
+                              users => \%user_cache, diffs => $diffs });
 
     # Find all those user-watching anyone on the current list, who is not
     # on it already themselves.

Bugzilla/Hook.pm

@@ -502,8 +502,17 @@ Every id in the incoming C<recipients> hash will have an object in here.
 (But if you add additional recipients to the C<recipients> hash, you are 
 B<not> required to add them to this hash.)
 
-=back
+=item C<diffs>
+
+This is a list of hashes, each hash representing a change to the bug. Each 
+hash has the following members: C<field_name>, C<bug_when>, C<old>, C<new> 
+and C<who> (a L<Bugzilla::User>). If appropriate, there will also be 
+C<attach_id> or C<comment_id>; if either is present, there will be 
+C<isprivate>. See C<_get_diffs> in F<Bugzilla/BugMail.pm> to see exactly how 
+it is populated. Warning: the format and existence of the "diffs" parameter 
+is subject to change in future releases of Bugzilla.
 
+=back
 
 =head2 bugmail_relationships