The functionality of Requests should be a core part of Connection.
Proposed migration path:
* add CreateChannel, Channels etc. to Connection with the same signatures and semantics as in Requests
* augment TpBaseConnection and the Python equivalent to implement both sets of D-Bus API
* when those changes are old enough to rely on, change MC (and any clients that go behind its back) to use the core Connection interface instead of Requests
* deprecate the methods and properties of the Requests interface (to avoid emitting three sets of signals, it's probably OK to not move the signals)
* in Telepathy 1.0 (Bug #23148), delete the Requests interface and move its signals to the core Connection
* when telepathy-glib API is broken, remove TpChannelFactoryIface and all code needed to support it
Telepathy 1.0 is relatively imminent and won't be backwards-compatible anyway, and porting will be straightforward, so let's just merge these interfaces at that point.