Log Message:
Update devel/libbson to 1.8.0.

- Make symbols bson_get_major_version, bson_get_minor_version,
  bson_get_micro_version, bson_get_version, and bson_check_version
  available to C++ programs.
- New CMake option ENABLE_MAINTAINER_FLAGS.
- Crash iterating over invalid code with scope.