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.