skip test_cwdx on Windows

cwd_x is explicitly disabled on Windows in prompts,
so it makes no sense to test it.

IPython/core/tests/test_prompts.py

@@ -98,6 +98,7 b' class PromptTests(unittest.TestCase):'
         self.assertEquals(format(lz), str(f))
         self.assertEquals(format(lz, '.1'), '0.5')
     
+    @dec.skip_win32
     def test_cwd_x(self):
         self.pm.in_template = r"\X0"
         save = os.getcwdu()