Generalize operator.indexOf (PySequence_Index) to work with any

iterable object.  I'm not sure how that got overlooked before!

Got rid of the internal _PySequence_IterContains, introduced a new
internal _PySequence_IterSearch, and rewrote all the iteration-based
"count of", "index of", and "is the object in it or not?" routines to
just call the new function.  I suppose it's slower this way, but the
code duplication was getting depressing.

Objects/classobject.c

@@ -1224,7 +1224,8 @@ instance_contains(PyInstanceObject *inst, PyObject *member)
 		 * __contains__ attribute, and try iterating instead.
 		 */
 		PyErr_Clear();
-		return _PySequence_IterContains((PyObject *)inst, member);
+		return _PySequence_IterSearch((PyObject *)inst, member,
+					      PY_ITERSEARCH_CONTAINS);
 	}
 	else
 		return -1;