The C++ standard reserves identifiers containing a double underscore (__) and identifiers that begin with an underscore followed by a capital letter A through Z (_[A-Z]). The codebase currently contains a few instances of these reserved identifiers. For instance,

https://github.com/mongodb/mongo/blob/r3.3.10/src/mongo/unittest/unittest.h#L103

We should clean up existing usages of reserved names and add a lint rule to enforce that they aren't added in the future.