This behavior allow to handle properly the case where an error
(such as a Broken Pipe error) is raised when reading on the socket.
When using SimpleServer class, the socket will be removed from the
connected client list. When using as client, the application is in charge
of re-connection exactly like a desired shutdown. A DEBUG logging message
is emitted by the library when this event is triggered.

RpcError are now reserved to rpc protocol, the RpcConnection uses the new
RpcConnectionError class.

NoFreeLabelError and FallbackModeEnabledError are now extending this new
class.