src: Refactoring common.hpp and minimizing exposed includes

Face class has relatively large rewrite to hide internals using
Implementor pattern.  As of this commit, <boost/asio.hpp> is not
automatically included whenever ndn-cxx/face.hpp is included.  If it is
needed to directly work with io_service, asio.hpp should be specifically
included.

Change-Id: Ie742b851025b4e3da634eb981319df0f42937855
diff --git a/tests/test-block.cpp b/tests/test-block.cpp
index bed9958..a4183f9 100644
--- a/tests/test-block.cpp
+++ b/tests/test-block.cpp
@@ -11,6 +11,7 @@
  */
 
 #include "encoding/encoding-buffer.hpp"
+#include "encoding/buffer-stream.hpp"
 
 #include "boost-test.hpp"