As soon as I moved to 1.7.0 and rewrote the code to use `mongoc_collection_find_with_opts()`, my filtering tests are starting to fail. Assuming we're working with this collection:

{_id: ..., "foo": "A"}
{_id: ..., "foo": "B"}
{_id: ..., "foo": "C"}
{_id: ..., "foo": "D"}

My pre-libmongoc-1.7.0 testing code used to construct the following filters (printed with `bson_as_json()` here) then pass them to `mongoc_collection_find()`:

`{ "$query" : { "opensips" : { "$lt" : "D" } } }`, gives 3 results. Correct.
`{ "$query" : { "$and" : [ { "foo" : { "$lt" : "D" } }, { "foo" : { "$gte" : "A" } } ] } }`, gives 3 results. Correct.

Now, I have updated the code to match the 1.7.0 API. Thanks to the new function, we can simplify the filters – here are the JSON views of the new filters, along with their results after passing them to the new `mongoc_collection_find_with_opts()`:

`{ "foo" : { "$lt" : "D" } }`, gives 3 results. Correct.
`{ "$and" : [ { "foo" : { "$lt" : "D" } }, { "foo" : { "$gte" : "A" } } ] }`, gives 0 results. Wrong!

Moreover, the 2nd query literally works if I hit it in the console, so either I'm doing something terribly wrong (forgetting some flag / API call / shouldn't be doing string comparisons anymore, etc.), or there is a good chance there is a bug in the 1.7.0 driver.

Any advice would be appreciated! Thanks!