OSX fix
Trac #16038: C function profiler

This ticket complements the `%prun` magic for Python profiler with a
`%crun` magic that given C function profile information using gperftools
(optional, expected to be provided by the OS).

URL: http://trac.sagemath.org/16038
Reported by: vbraun
Ticket author(s): Volker Braun
Reviewer(s): Nathann Cohen