(Follow-up to issue 14380)

The attached patch makes the email.mime.text.MIMEText constructor use the iso-8859-1 (aka latin-1) encoding for messages where all characters are in range(256). This also makes them use quoted-printable transfer encoding instead of base64.

So, the current algorithm of guessing encoding is as follows:

- all characters are in range(128) -> encoding is us-ascii
- all characters are in range(256) -> encoding is iso-8859-1 (aka latin-1)
- else                             -> encoding is utf-8