Export sends Content-Type twice

[Nazgul]

The export module sends the Content-Type header twice. Once as application/octet-stream, the other as text/xml.

header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header("Content-Disposition: attachment; filename=$filename");
header('Content-type: text/xml; charset=' . get_option('blog_charset'), true);

Fixed in [4563]

I don't believe that was causing any of the problems. The second header should have been overriding the first.

In my tests for [4563], that line (or its removal) didn't seem to effect any browser.