As detailed in
SERVER-27897, and the linked issues from there, unused RAII objects are often an indication of bugs. To avoid recurrence of this class of bugs, we need additional checking. As Max Hirschhorn noted, `clang-tidy` provides just that: http://clang.llvm.org/extra/clang-tidy/checks/misc-unused-raii.html
This ticket is to add such checking.