While investigating the warnings produced when compiling the C++ driver, we noticed that a large number of the warnings were actually in the libbson header files rather than from within our own source tree. Specifically, we found the following counts of errors when compiling with clang 3.9 on Linux and the flags `-Wall -Wextra -Wconversion -Wnarrowing -pedantic`:

555 macro expansion producing 'defined' has undefined behavior
555 implicit conversion changes signedness
222 implicit conversion loses integer precision