complex_coerce(): add explicit PyComplex_Check() test. Previously, complex_coerce() would never be called with a complex argument, because PyNumber_Coerce[Ex] doesn't bother calling the type's coercion method if the values already have the same type. But now, of course, it's possible to pass an instance of a complex *subtype*, and those must be accepted.

--- a/Objects/complexobject.c	Tue Sep 18 21:24:18 2001 +0000
+++ b/Objects/complexobject.c	Wed Sep 19 01:13:10 2001 +0000
@@ -538,6 +538,11 @@
 		Py_INCREF(*pv);
 		return 0;
 	}
+	else if (PyComplex_Check(*pw)) {
+		Py_INCREF(*pv);
+		Py_INCREF(*pw);
+		return 0;
+	}
 	return 1; /* Can't do it */
 }