Make sure code compiles on Ubuntu 12.04 with boost 1.46

Work with permissions in boost::filesystem was introduced in boost 1.49
diff --git a/server/server.hpp b/server/server.hpp
index b82088b..8a81b06 100644
--- a/server/server.hpp
+++ b/server/server.hpp
@@ -51,7 +51,7 @@
   boost::asio::io_service io_service_;
 
   /// The signal_set is used to register for process termination notifications.
-  boost::asio::signal_set signals_;
+  // boost::asio::signal_set signals_;
 
   /// Acceptor used to listen for incoming connections.
   boost::asio::ip::tcp::acceptor acceptor_;