This is primarily for backwards compatibility for when
or if the protocol is changed in future versions.
If the server fails to respond with an acceptable
protocol, the client disconnects and disables
the monitor.
We'll get `Errno::ECONNRESET` if the client forcibly disconnected.
Just close the socket rather than raising the exception.
Handle other errors in `ClientSocket#write`, too, mirroring the Faye
error handling which swallows all `StandardError` on write.
Before this commit, the `unsubscribed` callbacks in Action Cable server
side channels were never called. This is because when a WebSocket
"goodbye" message was sent from the client, the Action Cable server
didn't properly clean up after the now closed WebSocket. This means that
memory could possibly skyrocket with this behavior, since part of this
commit is to properly remove closed subscriptions from the global
subscriptions hash. Say you have 10,000 users currently connected, and
then all 10,000 disconnect -- before this patch, Action Cable would
still hold onto information (and Ruby objects!) for all of these now
dead connections.
