issue2551232 - modify in-reply-to threading when multiple matches if an email is missing an issue designator, in-reply-to threading is attempted. In this change if in-reply-to threading matches multiple issues, fall back to matching on subject. It used to just arbitrairly choose the first matching issue.

def audit_html_files(db, cl, nodeid, newvalues):
    if 'type' in newvalues and newvalues['type'] == 'text/html':
        newvalues['type'] = 'text/plain'
    

def init(db):
    db.file.audit('set', audit_html_files)
    db.file.audit('create', audit_html_files)