When moving old config files, don't clobber files we've previously moved.

IPython/utils/path.py

@@ -435,6 +435,10 b' def check_for_old_config(ipython_dir=None):'
                 os.unlink(f)
             else:
                 oldf = f+'.old'
+                i = 0
+                while os.path.exists(oldf):
+                    oldf = f+'.old.%i'%i
+                    i += 1
                 os.rename(f, oldf)
                 warn.warn("Renamed old IPython config file '%s' to '%s'." % (f, oldf))
                 warned = True