Accept header parsing fixes. Now return first acceptable match rather than last. If not acceptable match in accept, 406 error returns list of acceptable types as text string. application/xml is listed in acceptable types only if dicttoxml is installed. Handle q > 1.0 by demoting q factor to 0.0001 making it unusable. Test cases for all this code. XML is commented out as we don't install dicttoxml.py.

def init_severity(db, cl, nodeid, newvalues):
    """Make sure severity is set on new issues"""
    if 'severity' in newvalues and newvalues['severity']:
        return

    normal = db.severity.lookup('normal')
    newvalues['severity'] = normal

def init(db):
    db.issue.audit('create', init_severity)