TYPO3 Core

Can't configure the charset for htmlmail's, it's hardcoded to iso-88591-1.
I need it for emails generated from "Mail Form"s.
Emails are correct encoded, but the "Content-Type: ...; charset=iso-8859-1" doesn't match the encoding.
sv_htmlmailcharset is a good solution - I think it would make sense to use the value from config.metaCharset, but the extension was for version 3.5.0, not sure if it is compatible with 3.7.0.

This four lines cause the problem:
var $plain_text_header = "Content-Type: text/plain; charset=iso-8859-1\nContent-Transfer-Encoding: quoted-printable";
var $html_text_header = "Content-Type: text/html; charset=iso-8859-1\nContent-Transfer-Encoding: quoted-printable";
$this->plain_text_header = 'Content-Type: text/plain; charset=iso-8859-1'.chr(10).'Content-Transfer-Encoding: base64';
$this->html_text_header = 'Content-Type: text/html; charset=iso-8859-1'.chr(10).'Content-Transfer-Encoding: base64';

(issue imported from #M659)