added optional identifier argument to __init__; this is required to align with the  __reduce__ method
added optional identifier argument to __init__; this is required to align with the  __reduce__ method

git-svn-id: 60eb48102d1ca0c284ab3654bef916b01e1b221b@727 4f84a9ca-5c3e-0410-8a68-0bdf370325d5

nwebs/rdflib