[master] improve compression enabling logic

Author: oleksiys

providers/grizzly/src/main/java/org/asynchttpclient/providers/grizzly/GrizzlyAsyncHttpProvider.java

@@ -298,9 +298,10 @@ public void onTimeout(Connection connection) {
                 eventFilter.removeContentEncoding(encoding);
             }
         }
-        if (clientConfig.isCompressionEnforced()) {
-            eventFilter.addContentEncoding(new GZipContentEncoding(512, 512, new ClientEncodingFilter()));
-        }
+        
+        eventFilter.addContentEncoding(new GZipContentEncoding(512, 512,
+                new ClientEncodingFilter()));
+        
         secure.add(eventFilter);
         final AsyncHttpClientFilter clientFilter = new AsyncHttpClientFilter(this, clientConfig);
         secure.add(clientFilter);

providers/grizzly/src/main/java/org/asynchttpclient/providers/grizzly/filters/AsyncHttpClientFilter.java

@@ -513,6 +513,11 @@ private void addGeneralHeaders(final Request request, final HttpRequestPacket re
         if (!headers.contains(Header.UserAgent)) {
             requestPacket.addHeader(Header.UserAgent, config.getUserAgent());
         }
+        
+        if (config.isCompressionEnforced() &&
+                !headers.contains(Header.AcceptEncoding)) {
+            requestPacket.addHeader(Header.AcceptEncoding, "gzip");
+        }
     }
 
     private void addCookies(final Request request, final HttpRequestPacket requestPacket) {

providers/grizzly/src/main/java/org/asynchttpclient/providers/grizzly/filters/ClientEncodingFilter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Sonatype, Inc. All rights reserved.
+ * Copyright (c) 2013-2014 Sonatype, Inc. All rights reserved.
  *
  * This program is licensed to you under the Apache License Version 2.0,
  * and you may not use this file except in compliance with the Apache License Version 2.0.
@@ -30,7 +30,6 @@ public final class ClientEncodingFilter implements EncodingFilter {
     // --------------------------------------------- Methods from EncodingFilter
 
     public boolean applyEncoding(HttpHeader httpPacket) {
-        httpPacket.addHeader(Header.AcceptEncoding, "gzip");
         return false;
     }