build: Reviving support for precompiled headers

This commit also includes an update of ./waf, which has several
improvements.  In particular, clang++ is now default compiler on OSX
platform.

This commit also includes reorganization of tests. All unit tests are
now under tests/unit-tests and integrated tests are under
tests/integrated.  This change allows small compilation optimization,
partially related to precompiled headers.

Change-Id: I4c171c04d18e9cb83e461264a35b9ed85ea4d50e
diff --git a/src/common-pch.hpp b/src/common-pch.hpp
index 3d6c56f..b82f79d 100644
--- a/src/common-pch.hpp
+++ b/src/common-pch.hpp
@@ -41,10 +41,18 @@
 // Other useful headers to precompile
 #include <boost/lexical_cast.hpp>
 #include <boost/asio.hpp>
+#include <boost/chrono.hpp>
 #include <boost/date_time/posix_time/posix_time.hpp>
+#include <boost/property_tree/ptree.hpp>
+#include <boost/property_tree/info_parser.hpp>
+#include <boost/filesystem.hpp>
+#include <boost/regex.hpp>
+#include <boost/algorithm/string.hpp>
 
 #include <boost/iostreams/detail/ios.hpp>
 #include <boost/iostreams/categories.hpp>
 #include <boost/iostreams/stream.hpp>
 
+#include "security/cryptopp.hpp"
+
 #endif // NDN_COMMON_PCH_HPP