Should fix authentication issues.. server reflexive candidates have the same udp socket as their base host candidate.. we need to match all local candidates during stun agent validation

cast buf_len from size_t to int, as it might cause compilation issues with some versions of gcc, reported by dave_p_b from amsn's forums

Responses must be sent with the username and password, as if it was a new request we are sending. Do not use the username/password of the request we received

Adapt to the usages API and use a priv function to transform a niceAgent compatibility enum into a stun_usage_ice compatibility enum

Correctly set the priority for jingle and for msn compatibility (multiplied by 1000 so it can fit as an uint)

Use the proper magic cookie for ICE in msn compatibility mode and process the ice message without relying on stun/usages/bind.c