Doing it wrong:
Note the 'tr'; this is to avoid 8bit characters from appearing in the mail, which might otherwise be converted to their quoted-printable version in transit to the buildd; and since buildd-mail (the part that receives that mail) does not understand MIME, this would corrupt the GPG signature. This way, we do lose a few characters from the changelog, but that doesn't really matter -- the source still contains the unmodified changelog entry.
Doing it right.
Why, when we have access to all the sources, we still prefer hacks and workarounds over fixes? We are wasting our biggest advantage over propiertary systems!
Why #2 - do we still have to fight 7bit issues in email? Any mailer deployed in the last decade support passing 8bit mail fine. But, not all mailers (most usually, exim or qmail) support _converting_ 8bit mails to 7bit, and thus don't _advertize_ 8BITMIME capability. And when a properly 8BITMIME supporting mailer needs to pass a mail to a smtp daemon that doesn't advertize 8bit capability, the sending mail daemon will happily convert the mail to quoted printable mime. Graah.