src: minor updates to common.hpp and common-pch.hpp

Also remove redundant includes.

Change-Id: I0e1f55abcf852b95a4fd8c9a0e3a30aa153f892c
diff --git a/src/interest.cpp b/src/interest.cpp
index fa58a33..17a7aa4 100644
--- a/src/interest.cpp
+++ b/src/interest.cpp
@@ -24,6 +24,8 @@
 #include "util/crypto.hpp"
 #include "data.hpp"
 
+#include <cstring>
+
 namespace ndn {
 
 BOOST_CONCEPT_ASSERT((boost::EqualityComparable<Interest>));