security: Added SecurityException.what.
security: Added SecurityException.what.

cawka/packaging-ndn-cpp-dev,cawka/packaging-ndn-cpp,cawka/packaging-ndn-cpp-dev,cawka/packaging-ndn-cpp,cawka/packaging-ndn-cpp,cawka/packaging-ndn-cpp,cawka/packaging-ndn-cpp-dev,cawka/packaging-ndn-cpp-dev