show throw_out_of_range symbol

.travis.yml

@@ -105,6 +105,7 @@ script:
  - DURATION=2400
  - scripts/travis-command-wrapper.py -s "date" -i 120 --deadline=$(( $(date +%s) + ${DURATION} )) make
  - RESULT=0
+ - nm src/libmapnik.* | grep throw_out_of_range
  - make test || RESULT=$?
  # we allow visual failures with g++ for now: https://github.com/mapnik/mapnik/issues/3567
  - if [[ ${RESULT} != 0 ]] && [[ ${CXX} =~ 'clang++' ]]; then false; fi;