http: Prefer 'binary' over 'ascii'

It's faster, because it doesn't have to check that each char is in the
ASCII plane.

lib/_http_outgoing.js

@@ -122,7 +122,7 @@ OutgoingMessage.prototype._send = function(data, encoding, callback) {
       data = this._header + data;
     } else {
       this.output.unshift(this._header);
-      this.outputEncodings.unshift('ascii');
+      this.outputEncodings.unshift('binary');
       this.outputCallbacks.unshift(null);
     }
     this._headerSent = true;
@@ -421,7 +421,7 @@ OutgoingMessage.prototype.write = function(chunk, encoding, callback) {
 
       if (this.connection)
         this.connection.cork();
-      this._send(len.toString(16), 'ascii', null);
+      this._send(len.toString(16), 'binary', null);
       this._send(crlf_buf, null, null);
       this._send(chunk, encoding, null);
       ret = this._send(crlf_buf, null, callback);
@@ -507,10 +507,10 @@ OutgoingMessage.prototype.end = function(data, encoding, callback) {
   }
 
   if (this.chunkedEncoding) {
-    ret = this._send('0\r\n' + this._trailer + '\r\n', 'ascii', finish);
+    ret = this._send('0\r\n' + this._trailer + '\r\n', 'binary', finish);
   } else {
     // Force a flush, HACK.
-    ret = this._send('', 'ascii', finish);
+    ret = this._send('', 'binary', finish);
   }
 
   if (this.connection && data)