Description:
------------
The emails sent to subscribers of bug reports are lacking a
Content-Type header field. According to RFC 2045 section 5.2[1]
such messages are treated as with the default Content-Type:

  Content-type: text/plain; charset=us-ascii

This might cause MUAs to incorrectly display characters outside
the ASCII range.

Adding
  
  Content-Type: text/plain; charset=UTF-8
  
should solve the issue.

Furthermore the Content-Transfer-Encoding is missing, so according
to RFC 2045 section 6.1[2] it defaults to

  Content-Transfer-Encoding: 7bit
  
However, it should be

  Content-Transfer-Encoding: 8bit
  
[1] <https://tools.ietf.org/html/rfc2045#section-5.2>
[2] <https://tools.ietf.org/html/rfc2045#section-6.1>