Fixes #1085. The agent end event may call detachSocket() after the socket is detached and destroyed by abort(). This patch avoids that behavior.

lib/http.js

@@ -1333,7 +1333,10 @@ Agent.prototype._establishNewConnection = function() {
         debug('AGENT socket keep-alive');
       }
 
-      req.detachSocket(socket);
+      // The socket may already be detached and destroyed by an abort call
+      if (socket._httpMessage) {
+        req.detachSocket(socket);
+      }
 
       assert(!socket._httpMessage);