ndnping, nfd, repo-ng: Make sure that PKG_CONFIG_PATH variable is properly set towards macports

Change-Id: Idc480ef51d94dc8bc73f775065d8bef303945866
diff --git a/net/ndnping/Portfile b/net/ndnping/Portfile
index f6a13d2..6386417 100644
--- a/net/ndnping/Portfile
+++ b/net/ndnping/Portfile
@@ -13,7 +13,7 @@
 version             0.1.4
 license             GPL3+
 epoch               1
-revision            1
+revision            2
 
 categories          net
 platforms           darwin
@@ -30,6 +30,7 @@
 use_configure       yes
 
 configure.cxxflags-append -std=c++11
+configure.env-append PKG_CONFIG_PATH=${prefix}/lib/pkgconfig
 configure.cmd       ./waf configure
 
 build.cmd           ./waf