Initialize pth_list pointer to prevent AttributeError in imp.reload

pth_list_init.diff

diff -r 2c353e4e2488 Python/import.c
--- a/Python/import.c   Sun Jun 12 22:18:12 2011 +0200
+++ b/Python/import.c   Tue Jun 21 18:03:42 2011 -0400
@@ -3763,7 +3763,7 @@
     PyObject *modules_reloading = interp->modules_reloading;
     PyObject *modules = PyImport_GetModuleDict();
     PyObject *path_list = NULL, *loader = NULL, *existing_m = NULL;
-    PyObject *nameobj, *bufobj, *subnameobj, *pth_list;
+    PyObject *nameobj, *bufobj, *subnameobj, *pth_list = NULL;
     Py_UNICODE *name, *subname;
     struct filedescr *fdp;
     FILE *fp = NULL;