Python interpreter.

This change adds two new C-level APIs:  PyEval_SetProfile() and
PyEval_SetTrace().  These can be used to install profile and trace
functions implemented in C, which can operate at much higher speeds
than Python-based functions.  The overhead for calling a C-based
profile function is a very small fraction of a percent of the overhead
involved in calling a Python-based function.

The machinery required to call a Python-based profile or trace
function been moved to sysmodule.c, where sys.setprofile() and
sys.setprofile() simply become users of the new interface.

As a side effect, SF bug #436058 is fixed; there is no longer a
_PyTrace_Init() function to declare.