Fix 204 responses, hangs and crashes with REST. Remove Content-Type and make sure no content is returned by OPTIONS request in REST interface. In write_html set the Content-Length when response is not encoded/compressed (fixes hang due to missing content-length with unencoded data). In REST interface do not raise UsageError for invalid api version. Return json error with proper message. Fixes crash.

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)