Don't override connection header if Upgrading

Author: jayharris

lib/http-proxy/common.js

@@ -47,12 +47,14 @@ common.setupOutgoing = function(outgoing, options, req, forward) {
   outgoing.localAddress = options.localAddress;
 
   //
-  // Remark: If we are false set the connection: close. This is the right thing to do
+  // Remark: If we are false and not upgrading, set the connection: close. This is the right thing to do
   // as node core doesn't handle this COMPLETELY properly yet.
   //
   if(!outgoing.agent) {
     outgoing.headers = outgoing.headers || {};
-    outgoing.headers.connection = 'close';
+    if(typeof outgoing.headers.connection !== 'string' || outgoing.headers.connection.toLowerCase() !== 'upgrade') {
+      outgoing.headers.connection = 'close';
+    }
   }
 
   //