CDRIVER-2128 test parsing legacy $regex
CDRIVER-2128 test parsing legacy $regex

rcsanchez97/libbson,mongodb/libbson,mapr/libbson,mongodb/libbson,rcsanchez97/libbson,mongodb/libbson,mapr/libbson,ajdavis/libbson,ajdavis/libbson,rcsanchez97/libbson,mapr/libbson,ajdavis/libbson