lei mail-diff: diagnostic command to diff mail contents

This is useful in finding the cause of deduplication bugs,
and possibly the cause of missing threads reported by
Konstantin in <20211001130527.z7eivotlgqbgetzz@meerkat.local>

usage:

  u=https://yhbt.net/lore/all/87czop5j33.fsf@tynnyri.adurom.net/raw
  lei mail-diff $u

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/PublicInbox/LeiInput.pm b/lib/PublicInbox/LeiInput.pm
index 22bedba6..83479221 100644
--- a/lib/PublicInbox/LeiInput.pm
+++ b/lib/PublicInbox/LeiInput.pm
@@ -57,6 +57,12 @@ sub check_input_format ($;$) {
         1;
 }
 
+sub input_mbox_cb { # base MboxReader callback
+        my ($eml, $self) = @_;
+        $eml->header_set($_) for (qw(Status X-Status));
+        $self->input_eml_cb($eml);
+}
+
 # import a single file handle of $name
 # Subclass must define ->input_eml_cb and ->input_mbox_cb
 sub input_fh {