build: Disable ndnboost installation when system-installed Boost libraries are selected with --use-system-boost configure option

Change-Id: Iad0f9fb45bfa5c95d90b8ee9bfb07aa4cf2babc8
diff --git a/configure.ac b/configure.ac
index 9d6a355..33b5696 100644
--- a/configure.ac
+++ b/configure.ac
@@ -70,9 +70,12 @@
   [
     if test "$want_system_boost" == "yes" ; then
       AC_DEFINE(USE_SYSTEM_BOOST,[1],[use system-installed boost libraries])
+      AM_CONDITIONAL(USE_SYSTEM_BOOST, true)
+    else
+      AM_CONDITIONAL(USE_SYSTEM_BOOST, false)
     fi
   ],
-  []
+  [AM_CONDITIONAL(USE_SYSTEM_BOOST, false)]
 )
 AX_BOOST_ASIO
 
diff --git a/include/Makefile.am b/include/Makefile.am
index b38a6d4..2f0a01d 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -194,4 +194,8 @@
   $(wildcard ndnboost/lambda/*.*) \
   $(wildcard ndnboost/lambda/detail/*.*)
 
-nobase_include_HEADERS = $(ndn_cpp_c_headers) $(ndn_cpp_cpp_headers) $(ndnboost_headers)
+nobase_include_HEADERS = $(ndn_cpp_c_headers) $(ndn_cpp_cpp_headers)
+
+if ! USE_SYSTEM_BOOST
+  nobase_include_HEADERS += $(ndnboost_headers)
+endif