Log Message:
Update databases/mongo-c-driver to 1.5.3.

Changes since 1.5.0:

- allow mixed $ and non-$ query ops.
- Missing exports of mongoc_gridfs_file_set_*() functions.
- update define constants for "find" opts to be unique.
- Windows CA stores should be opened with read-only flag.
- Fix SEGFAULT with performance counters on NUMA (thanks to Jonathan Wang).
- Prevent rare assertion error in mongoc_cluster_stream_for_server.
- Improve error messages from auth failure.
- Escape quotes when appending CFLAGS to handshake metadata.
- Fix OpenSSL header lookups in non-default paths.
- Fix build failure with LibreSSL.