There have been a few recent cases seen where we have not been properly cleaning up after initializing bson_t (see CDRIVER-2308). There may be some additional cases where we aren't cleaning up a bson_t, but it isn't showing up in valgrind because it isn't spilling over to the heap. To prevent this from happening again, we should add a compile flag to enforce every bson_init and BSON_INITIALIZER allocates memory. This should help us discover misuse of bson_t's, and will prevent real memory leaks from happening when they do spill over. We should add a flag in cmake and our autoconf configuration to enable this.