parsers: statically initializing tp_new to PyType_GenericNew is not portable

As detailed on http://docs.python.org/extending/newtypes.html (quote):

  "In this case, we can just use the default implementation provided by the API
  function PyType_GenericNew(). We’d like to just assign this to the
  tp_new slot, but we can’t, for portability sake. On some platforms or
  compilers, we can’t statically initialize a structure member with a function
  defined in another C module, so, instead, we’ll assign the tp_new slot in the
  module initialization function just before calling PyType_Ready()."

Fixes "gcc (GCC) 3.4.5 (mingw-vista special r3)" complaining with:

  mercurial/parsers.c:1096: error: initializer element is not constant
  mercurial/parsers.c:1096: error: (near initialization for `indexType.tp_new')

mercurial/parsers.c

@@ -1092,7 +1092,6 b' static PyTypeObject indexType = {'
 	0,                         /* tp_dictoffset */
 	(initproc)index_init,      /* tp_init */
 	0,                         /* tp_alloc */
-	PyType_GenericNew,         /* tp_new */
 };
 
 /*
@@ -1150,6 +1149,7 b' static PyMethodDef methods[] = {'
 
 static void module_init(PyObject *mod)
 {
+	indexType.tp_new = PyType_GenericNew;
 	if (PyType_Ready(&indexType) < 0)
 		return;
 	Py_INCREF(&indexType);