Change #include style

Header files are now always included with their path from the
project's root directory rather than the path relative to
the includer.

Change-Id: If39b8510eef8da00baf5fe88337c45dbdf8c766e
Refs: #3084
diff --git a/tests/unit/util/placeholders.t.cpp b/tests/unit/util/placeholders.t.cpp
index 0dc8c70..16dece5 100644
--- a/tests/unit/util/placeholders.t.cpp
+++ b/tests/unit/util/placeholders.t.cpp
@@ -22,11 +22,11 @@
 // Bug 2109 test case
 
 // interest.hpp includes common.hpp; common.hpp shouldn't be used from external program
-#include "interest.hpp"
+#include "ndn-cxx/interest.hpp"
 
 // util/config-file.hpp indirectly includes <boost/property_tree/ptree.hpp>
 // which in turn imports Boost placeholders
-#include "util/config-file.hpp"
+#include "ndn-cxx/util/config-file.hpp"
 
 // It's intentional to write "using namespace",
 // to simulate an external program linked against ndn-cxx.