Update gem dependencies.
More robust “safe” option switch.

Compare Mongo::VERSION instead of using MongoClient class existence.
Update compiled genghis.*
Get API spec passing.

We’ll ignore the issues with encoded slashes in the URL for now. Unfortunately, it looks like rack-protect is joining Apache in making the exact wrong call in this case :(
Bump to v2.3.9
Merge branch 'release/2.3.9' into develop