security: Added headers for der encoding.  Added CertificateExtension and CertificateSubjectDescription.
diff --git a/include/Makefile.am b/include/Makefile.am
index 06d98aa..8ea2630 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -34,6 +34,8 @@
   ndn-cpp/security/security-common.hpp \
   ndn-cpp/security/key-chain.hpp \
   ndn-cpp/security/security-exception.hpp \
+  ndn-cpp/security/certificate/certificate-extension.hpp \
+  ndn-cpp/security/certificate/certificate-subject-description.hpp \
   ndn-cpp/security/certificate/certificate.hpp \
   ndn-cpp/security/certificate/identity-certificate.hpp \
   ndn-cpp/security/certificate/public-key.hpp \