trychange.py: make --sub_rep work again

trychange.py

Index: trychange.py
===================================================================
--- trychange.py	(revision 116575)
+++ trychange.py	(working copy)
@@ -696,8 +696,10 @@
     checkouts.append(GuessVCS(options, path, file_list))
     checkouts[0].AutomagicalSettings()
     for item in options.sub_rep:
-      checkout = GuessVCS(options, os.path.join(checkouts[0].checkout_root,
-                                                item), file_list)
+      # Pass file_list=None because we don't know the sub repo's file list.
+      checkout = GuessVCS(options,
+                          os.path.join(checkouts[0].checkout_root, item),
+                          None)
       if checkout.checkout_root in [c.checkout_root for c in checkouts]:
         parser.error('Specified the root %s two times.' %
                      checkout.checkout_root)