Update databases/mongo-c-driver to 1.5.0.

New features and bug fixes:

- MongoDB 3.4 Support
  - New URI and read preference option, "maxStalenessSeconds"
  - Set MongoDB client handshake data with mongoc_client_set_appname or
    mongoc_client_pool_set_appname.
  - writeConcern and readConcern enhancements.
  - Collation allows users to specify language-specific rules for string
    comparison when sorting documents.
- mongoc_collection_count_with_opts uses the collection's read
  preference if none is passed in
- Improved TLS support
  - Fixed LibreSSL (libssl) support
  - Added LibreSSL (libtls) support
  - Fixed Secure Channel build on VS 2010
  - OpenSSL now supports SNI (all others already do)
- Additional features for Application Performance Monitoring
- New functions accept flexible options as a BSON document.
- mongoc_collection_find is now deprecated in favor of
  mongoc_collection_find_with_opts.
- New helper function to include read concern in one of the above
  function's options parameter: mongoc_read_concern_append.
- mongoc_client_command no longer applies the client's read preference
  and read concern by default. Same change for mongoc_database_command
  and mongoc_collection_command.
- mongoc_collection_count_with_opts now applies the collection's read
  preference if no read preference is provided
- mongoc_collection_create_index and mongoc_collection_drop_index now
  apply the collection's write concern.
- mongoc_collection_create_index_with_opts now applies the collection's
  write concern if none is specified in "opts"
- connectTimeoutMS timer now begins after DNS resolution, and resets for
  each interface attempted (e.g., if the driver first tries IPv6, then
  IPv4).
- New error code MONGOC_ERROR_DUPLICATE_KEY.
- mongoc_collection_find no longer treats the "filter" key specially in
  queries - querying for a document with a key named "filter" is the
  same now as any other key.
- The server description parameter to the following functions is
  "const":
  - mongoc_server_description_host
  - mongoc_server_description_id
  - mongoc_server_description_ismaster
  - mongoc_server_description_round_trip_time
  - mongoc_server_description_type
- Exported symbols are no longer declared in seperate export files.
- mongoc no longer crashes when multi roundtrip bulk operation fails.
- Added support for the new readConcernLevel "linearizable".
- Clients now check for misformatted "readPreferenceTags" in URI.
- New CMake option ENABLE_TRACING allows debug output, which before had
  only been available with "configure --enable-tracing".
- Bugfix: "PossiblePrimary"-type replicas could be selected for reads
- Bugfixes: The random number generator used to select servers is now
  properly seeded, and secondary queries are now properly distributed
  according to localThresholdMS, not just to the lowest-latency secondary.
  The latency estimate is reset after a connection error.
- Fix crashes in mongoc_topology_invalidate_server and
  mongoc_client_kill_cursor.
- mongoc_collection_insert, mongoc_collection_update,
  mongoc_collection_remove consistently use domain MONGOC_ERROR_BSON,
  code MONGOC_ERROR_BSON_INVALID if passed oversized BSON, and
  MONGOC_ERROR_COLLECTION for other errors. mongoc_bulk_operation_execute
  continues to use MONGOC_ERROR_COMMAND for all errors.
- If mongoc_client_pool_t fails to start its scanner thread in the
  background, it logs and aborts instead of silently continuing, then
  failing to connect.
- The driver now updates its view of the whole topology with information
  from each new connection handshake.
- Improved error reporting when the driver fails to reach the server,
  and correctly distinguish "connection error" and "connection timeout".

Deprecations:

- mongoc_collection_find is deprecated for
  mongoc_collection_find_with_opts.

Removed configure flags:

- --enable-experimental has been removed. All previously experimental
  features are now always on.
- The configure option "--enable-hardening" had had no effect. It is
  removed in favor of system-wide compiler configuration.

(fhajny)