Issue #3327: Don't overallocate in the modules_by_index list.

Misc/NEWS

@@ -13,6 +13,8 @@ What's New in Python 3.0 release candiate 3?
 Core and Builtins
 -----------------
 
+- Issue #3327: Don't overallocate in the modules_by_index list.
+
 - Issue #1721812:  Binary set operations and copy() returned the input type
   instead of the appropriate base type.  This was incorrect because set 
   subclasses would be created without their __init__() method being called.

Python/pystate.c

@@ -234,7 +234,7 @@ _PyState_AddModule(PyObject* module, struct PyModuleDef* def)
 	if (!def)
 		return -1;
 	if (!state->modules_by_index) {
-		state->modules_by_index = PyList_New(20);
+		state->modules_by_index = PyList_New(0);
 		if (!state->modules_by_index)
 			return -1;
 	}