call_trace(): Add an additional parameter -- pointer to a PyObject* that should be used to cache an interned version of the event string passed to the profile/trace function. call_trace() will create interned strings and cache them in using the storage specified by this additional parameter, avoiding a lot of string object creation at runtime when using the profiling or tracing functions. All call sites are modified to pass the additional parameter, and four static PyObject* variables are allocated to cache the interned string objects. This closes SF patch #431257.