build: Experimental support to build using precompiled headers

This type of build needs to be explicitly enabled using --with-pch
configure option.

Change-Id: I02dc304187d54c3cf40f1d51b1b11b21f868e225
diff --git a/src/util/crypto.cpp b/src/util/crypto.cpp
index 490feb8..8967523 100644
--- a/src/util/crypto.cpp
+++ b/src/util/crypto.cpp
@@ -4,7 +4,9 @@
  * See COPYING for copyright and distribution information.
  */
 
-#include "util/crypto.hpp"
+#include "common.hpp"
+
+#include "crypto.hpp"
 
 namespace ndn {
 
diff --git a/src/util/logging.cpp b/src/util/logging.cpp
index 7147768..59c7b2a 100644
--- a/src/util/logging.cpp
+++ b/src/util/logging.cpp
@@ -6,6 +6,8 @@
  * See COPYING for copyright and distribution information.
  */
 
+#include "common.hpp"
+
 #include "logging.hpp"
 
 #ifdef NDN_CPP_HAVE_LOG4CXX
diff --git a/src/util/random.cpp b/src/util/random.cpp
index f1cb5b9..6bbe203 100644
--- a/src/util/random.cpp
+++ b/src/util/random.cpp
@@ -4,6 +4,8 @@
  * See COPYING for copyright and distribution information.
  */
 
+#include "common.hpp"
+
 #include "random.hpp"
 
 #include <cryptopp/osrng.h>
diff --git a/src/util/scheduler.cpp b/src/util/scheduler.cpp
index c13e070..388d5e7 100644
--- a/src/util/scheduler.cpp
+++ b/src/util/scheduler.cpp
@@ -4,6 +4,8 @@
  * See COPYING for copyright and distribution information.
  */
 
+#include "common.hpp"
+
 #include "scheduler.hpp"
 
 namespace ndn {
diff --git a/src/util/time.cpp b/src/util/time.cpp
index 97ac14c..07e7f34 100644
--- a/src/util/time.cpp
+++ b/src/util/time.cpp
@@ -4,6 +4,8 @@
  * See COPYING for copyright and distribution information.
  */
 
+#include "common.hpp"
+
 #include "time.hpp"
 #include <time.h>
 #include <stdexcept>
diff --git a/src/util/time.hpp b/src/util/time.hpp
index 9af95fc..5d729d9 100644
--- a/src/util/time.hpp
+++ b/src/util/time.hpp
@@ -9,7 +9,6 @@
 #define NDN_TIME_HPP
 
 #include "../common.hpp"
-#include <boost/date_time/posix_time/posix_time.hpp>
 
 namespace ndn {