fix SyntaxError on !(command)

prefilter_line expects that trailing newlines will be trimmed, but
run_cell passed it lines with a trailing \n.

Single-line run_cell now uses prefilter_lines again, and appends newline explicitly.

Formerly failing test included.

IPython/core/interactiveshell.py

@@ -2172,7 +2172,9 b' class InteractiveShell(SingletonConfigurable, Magic):'
             prefilter_failed = False
             if len(cell.splitlines()) == 1:
                 try:
-                    cell = self.prefilter_manager.prefilter_line(cell)
+                    # use prefilter_lines to handle trailing newlines
+                    # restore trailing newline for ast.parse
+                    cell = self.prefilter_manager.prefilter_lines(cell) + '\n'
                 except AliasError as e:
                     error(e)
                     prefilter_failed=True

IPython/core/tests/test_interactiveshell.py

@@ -106,4 +106,11 b' class InteractiveShellTestCase(unittest.TestCase):'
         err = io.stderr.getvalue()
         io.stderr = save_err
         self.assertEquals(err.split(':')[0], 'ERROR')
+    
+    def test_trailing_newline(self):
+        """test that running !(command) does not raise a SyntaxError"""
+        ip = get_ipython()
+        ip.run_cell('!(true)\n', False)
+        ip.run_cell('!(true)\n\n\n', False)
+