SERVER-13528 Cherry pick fixes for gperftools issue 581

https://code.google.com/p/gperftools/source/detail?r=185bf3fcc36f8cb3839abdfe652f615bfb5306d1
https://code.google.com/p/gperftools/source/detail?r=71a239e559c9ea2300ad0511f8de7077db5369c3
SERVER-13528 After taking gperftools issue 581 fixes, renable OS X debug alloc