Fix Python 3 issues in REST code. * Need to use .get not .getheader for HTTP headers (see hg commit fec18298ae02, "Python 3 preparation: HTTP headers handling in roundup_server.py."). * Need to use key not cmp with sort (see hg commit 3fa026621f69, "Python 3 preparation: comparisons."). * dispatch output must be bytes, not str, otherwise writing it to the socket (e.g. in roundup-server) will fail. This fixes issues shown up attempting to access the REST interface with a browser with Python 3 (as opposed to with the Roundup testsuite, which also has known REST issues with Python 3).

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)