When trying to use the C driver (embedded in Rust via https://github.com/thijsc/mongo-rust-driver) together with other code that uses OpenSSL connections fail.

Everything works up until initialization of an OpenSSL context by another library. Then the trace below happens and connections fail.

Is this a bug in the Mongo C driver? Should we maybe be using SSL_CTX_get_ex_new_index for example to scope the callbacks to just the C driver itself?

```
[2015-09-01T09:33:31][TRACE] mongoc: cursor - ENTRY: mongoc_cursor_more():875
[2015-09-01T09:33:31][TRACE] mongoc: cursor - EXIT: mongoc_cursor_more():885
[2015-09-01T09:33:31][TRACE] mongoc: cursor - ENTRY: mongoc_cursor_next():741
[2015-09-01T09:33:31][TRACE] mongoc: cursor - TRACE: mongoc_cursor_next():746 cursor_id(0)
[2015-09-01T09:33:31][TRACE] mongoc: cursor - ENTRY: _mongoc_cursor_next():777
[2015-09-01T09:33:31][TRACE] mongoc: cursor - ENTRY: _mongoc_cursor_query():476
[2015-09-01T09:33:31][TRACE] mongoc: cluster - ENTRY: _mongoc_cluster_reconnect():2537
[2015-09-01T09:33:31][TRACE] mongoc: cluster - ENTRY: _mongoc_cluster_update_state():115
[2015-09-01T09:33:31][TRACE] mongoc: cluster - EXIT: _mongoc_cluster_update_state():142
[2015-09-01T09:33:31][TRACE] mongoc: cluster - ENTRY: _mongoc_cluster_reconnect_replica_set():2205
[2015-09-01T09:33:31][DEBUG] mongoc: cluster - Reconnecting to replica set.
[2015-09-01T09:33:31][TRACE] mongoc: cluster - ENTRY: _mongoc_cluster_clear_peers():208
[2015-09-01T09:33:31][TRACE] mongoc: cluster - EXIT: _mongoc_cluster_clear_peers():216
[2015-09-01T09:33:31][TRACE] mongoc: client - ENTRY: mongoc_client_connect_tcp():90
[2015-09-01T09:33:31][TRACE] mongoc: socket - ENTRY: mongoc_socket_new():609
[2015-09-01T09:33:31][TRACE] mongoc: socket - ENTRY: _mongoc_socket_setnodelay():182
[2015-09-01T09:33:31][TRACE] mongoc: socket - EXIT: _mongoc_socket_setnodelay():194
[2015-09-01T09:33:31][TRACE] mongoc: socket - EXIT: mongoc_socket_new():633
[2015-09-01T09:33:31][TRACE] mongoc: socket - ENTRY: mongoc_socket_connect():472
[2015-09-01T09:33:31][TRACE] mongoc: socket - ENTRY: _mongoc_socket_wait():123
[2015-09-01T09:33:31][TRACE] mongoc: socket - EXIT: _mongoc_socket_wait():160
[2015-09-01T09:33:31][TRACE] mongoc: socket - EXIT: mongoc_socket_connect():497
[2015-09-01T09:33:31][WARN] mongoc: cluster - Failed connection to mongo1.staging:27017
```