The FaultTolerantNegotiator is the reason why Smack replies in a
non-standard way to file transfer requests: Smack puts two values in
the stream-method field, while the field is a list-single field,
i.e. a field which only allows one value.
Even if what Smack does is probably better, as it allows for a
fallback in case the bytestream transport fails, it is not standard
compliant. And, Jingle provide a proper fallback specification for
file transfers.
Fixes SMACK-561.