use more robust quoting

Lib/test/test_popen.py

@@ -17,7 +17,7 @@ python = sys.executable
 
 class PopenTest(unittest.TestCase):
     def _do_test_commandline(self, cmdline, expected):
-        cmd = '%r -c "import sys;print sys.argv" %s' % (python, cmdline)
+        cmd = '"%s" -c "import sys;print sys.argv" %s' % (python, cmdline)
         data = os.popen(cmd).read()
         got = eval(data)[1:] # strip off argv[0]
         self.assertEqual(got, expected)