fix two bugs of GraphAPIError

Hi there,

I fixed two bugs of GraphAPIError.

### Wrongly paring of error response

with the commit 0f28100.

Test:

    from facebook import GraphAPI, GraphAPIError
    from pprint import pprint

    graph = GraphAPI(access_token='123')

    try:
        graph.get_object('me')
    except GraphAPIError, e:
        print 'e.type: %r' % e.type
        print 'e.result:'
        pprint(e.result)

Result before fixed:

    e.type: ''
    e.result:
    {'error': {'code': 190,
               'message': 'Invalid OAuth access token.',
               'type': 'OAuthException'}}

Result after fixed:

    e.type: 190
    e.result:
    {'error': {'code': 190,
               'message': 'Invalid OAuth access token.',
               'type': 'OAuthException'}}

### Wrong parameters for GraphAPIError

Please see the commit fffe690.