Enable test for cells ending in multiline strings, as it now passes.

Closes gh-306

IPython/core/tests/test_interactiveshell.py

@@ -56,7 +56,6 b' class InteractiveShellTestCase(unittest.TestCase):'
         self.assertEquals(ip.user_ns['x'], 2)
         self.assertEquals(ip.user_ns['y'], 3)
 
-    @dec.skip_known_failure
     def test_multiline_string_cells(self):
         "Code sprinkled with multiline strings should execute (GH-306)"
         ip = get_ipython()