Rename broadcast to transmit for the connection/channel->subscriber communication

Disambiguate it from the broadcast to channel method used by the
broadcaster (which actually has several listeners, whereas a
connection/channel instance only ever has one listener – hence not much
of a BROADcast).

lib/action_cable/channel/base.rb

@@ -79,10 +79,10 @@ def disconnect
         end
 
 
-        def broadcast(data)
+        def transmit(data, via: nil)
           if authorized?
-            logger.info "#{channel_name} broadcasting #{data.inspect}"
-            connection.broadcast({ identifier: @channel_identifier, message: data }.to_json)
+            logger.info "#{channel_name} transmitting #{data.inspect} #{via}"
+            connection.transmit({ identifier: @channel_identifier, message: data }.to_json)
           else
             unauthorized
           end

lib/action_cable/channel/redis.rb

@@ -29,8 +29,7 @@ def unsubscribe_from_all_channels
       protected
         def default_subscription_callback(channel)
           -> (message) do
-            logger.info "Received a message over the redis channel: #{channel}"
-            broadcast ActiveSupport::JSON.decode(message)
+            transmit ActiveSupport::JSON.decode(message), via: "incoming action from #{channel}"
           end
         end
     end

lib/action_cable/connection/base.rb

@@ -34,8 +34,8 @@ def process
           @websocket = Faye::WebSocket.new(@env)
 
           @websocket.on(:open) do |event|
-            broadcast_ping_timestamp
-            @ping_timer = EventMachine.add_periodic_timer(PING_INTERVAL) { broadcast_ping_timestamp }
+            transmit_ping_timestamp
+            @ping_timer = EventMachine.add_periodic_timer(PING_INTERVAL) { transmit_ping_timestamp }
             worker_pool.async.invoke(self, :initialize_connection)
           end
 
@@ -87,7 +87,7 @@ def cleanup_subscriptions
         end
       end
 
-      def broadcast(data)
+      def transmit(data)
         @websocket.send data
       end
 
@@ -127,8 +127,8 @@ def on_connection_closed
           disconnect if respond_to?(:disconnect)
         end
 
-        def broadcast_ping_timestamp
-          broadcast({ identifier: '_ping', message: Time.now.to_i }.to_json)
+        def transmit_ping_timestamp
+          transmit({ identifier: '_ping', message: Time.now.to_i }.to_json)
         end
 
         def subscribe_channel(data)