Log Message:
Update databases/mongo-c-driver to 1.8.0.

- The zLib and Snappy compression libraries are bundled if not
  available.
  Wire protocol compression is enabled on Windows.
- mongoc_collection_find_and_modify_with_opts now respects a
  "writeConcern" field in the "extra" BSON document in its
  mongoc_find_and_modify_opts_t.
- The command functions mongoc_client_read_write_command_with_opts,
  mongoc_database_read_write_command_with_opts, and
  mongoc_collection_read_write_command_with_opts now ignore the
  "read_prefs" parameter.
- mongoc_collection_create_index and
  mongoc_collection_create_index_with_opts
  are both now deprecated. Use mongoc_database_write_command_with_opts
  instead; a guide to creating an index using that function has been
  added.
- Use select, not WSAPoll, on Windows.
- Always mark a server "Unknown" after a network error (besides a
  timeout).
- mongoc_client_pool_t sends platform metadata to the server; before,
  only a single mongoc_client_t did.
- New stream method mongoc_stream_timed_out.
- Wire version checks introduced in 1.8.0 will prevent the driver from
  connecting to a future MongoDB server version if its wire protocol is
  incompatible.
- New CMake option ENABLE_MAINTAINER_FLAGS.