Make sure FileRegion.releaseExternalResources() is called after the

write was done. See NETTY-440

src/main/java/org/jboss/netty/channel/socket/nio/SocketSendBufferPool.java

@@ -288,7 +288,8 @@ final class SocketSendBufferPool {
         }
 
         public void release() {
-            // Unpooled.
+            // Make sure the FileRegion resource are released otherwise it may cause a FD leak or something similar
+            file.releaseExternalResources();
         }
     }