xla

1de9c055 - Changed the computation client interface to be compile handle based to get around the continuous marshaling of computation protos.

Changed the computation client interface to be compile handle based to get around the continuous marshaling of computation protos. Unfortunately this means abandoning the XLA interface, as it does not support the kind of semantics. The XLA interface was crippled anyway, since the Replicated execution was not supported either. Given that we are thinking of exposing more TF bits in order to achieve better performance, going full XRT is the only way to go.