Fix a crasher where Python code managed to infinitely recurse in C code without

ever going back out to Python code in PyObject_Call().  Required introducing a
static RuntimeError instance so that normalizing an exception there is no
reliance on a recursive call that would put the exception system over the
recursion check itself.

Include/pyerrors.h

@@ -161,6 +161,7 @@ PyAPI_DATA(PyObject *) PyExc_VMSError;
 #endif
 
 PyAPI_DATA(PyObject *) PyExc_MemoryErrorInst;
+PyAPI_DATA(PyObject *) PyExc_RecursionErrorInst;
 
 /* Predefined warning categories */
 PyAPI_DATA(PyObject *) PyExc_Warning;