some changes for SpdyPersistentUrl:
some changes for SpdyPersistentUrl:

 - make it a runtime error to set certain inherited callback properties (used internally by this class)
 - be stricter about usage of 'super' vs 'self'
 - use the new isConnecting property of SpdyRequest in sendPing and in reconnect

locationlabs/SPDY-for-iPhone,locationlabs/SPDY-for-iPhone