Fix SF #763362, test_posixpath failed

Don't check expanduser('~') if the home directory == the root directory
(ie, we are running as root).

Lib/test/test_posixpath.py

@@ -338,6 +338,8 @@ class PosixPathTest(unittest.TestCase):
             pass
         else:
             self.assert_(isinstance(posixpath.expanduser("~/"), basestring))
+            # if home directory == root directory, this test makes no sense
+            if posixpath.expanduser("~") != '/':
                 self.assertEqual(
                     posixpath.expanduser("~") + "/",
                     posixpath.expanduser("~/")