ndn-cxx: Add conflict with ndn.cxx-security-tools package

Fixes: #3
diff --git a/ndn-cxx/debian/control b/ndn-cxx/debian/control
index 1a42dfa..ac8f52b 100644
--- a/ndn-cxx/debian/control
+++ b/ndn-cxx/debian/control
@@ -32,3 +32,4 @@
 Architecture: i386 amd64
 Depends: ${shlibs:Depends}, ${misc:Depends}
 Description: NDN C++ library with eXperimental eXtensions and security tools
+Conflicts: ndn.cxx-security-tools