util: work around behavior change in Python 2.7.1

mercurial/util.py

@@ -391,7 +391,8 b' def system(cmd, environ={}, cwd=None, on'
             return '1'
         return str(val)
     origcmd = cmd
-    if os.name == 'nt':
+    if os.name == 'nt' and sys.version_info < (2, 7, 1):
+        # Python versions since 2.7.1 do this extra quoting themselves
         cmd = '"%s"' % cmd
     env = dict(os.environ)
     env.update((k, py2shell(v)) for k, v in environ.iteritems())