HandleChannels: provide request-properties, as for ObserveChannels
HandleChannels: provide request-properties, as for ObserveChannels

Guillaume thinks this is useful even though it's somewhat redundant with
Client.I.Requests. I'm inclined to agree, because handlers with
Client.I.Requests are woken up as soon as possible for a request that
might end up failing, and not all handlers want to deal with that.

TelepathyIM/telepathy-spec,freedesktop-unofficial-mirror/telepathy__telepathy-spec