This reverts commit f50ba06.
If the proxy client disconnects before the server connects or sends data, a proxy_connect_error or proxy_inactivity_error was fired because the client connection closes the server connection. This patch causes the server to check that the client is still available before assuming a connect/inactivity error.
This can happen when there's some kind of load balancer or proxy between the proxymachine and the real server. The balancer accepts the connection and then immediately disconnects instead of rejecting the connection outright.
The removed try_server_connect logic will never fail because of EM's asynchronous nature. The ServerConnection.request, EM.connect, and proxy_incoming_to calls will always complete without exception because the actual socket operations don't take place until a future tick. In order to support connect failure detection and retries, we'll need to hook into the ServerConnection#connection_completed callback.