prevent errors in prefilter from crashing IPython

closes gh-216

IPython/core/interactiveshell.py

@@ -2130,7 +2130,20 b' class InteractiveShell(Configurable, Magic):'
         
         with self.builtin_trap:
             if len(cell.splitlines()) == 1:
+                try:
                 cell = self.prefilter_manager.prefilter_lines(cell)
+                except Exception:
+                    # don't allow prefilter errors to crash IPython, because
+                    # user code can be involved (e.g. aliases)
+                    self.showtraceback()
+                    if store_history:
+                        self.history_manager.store_inputs(self.execution_count, 
+                                                          cell, raw_cell)
+
+                    self.logger.log(cell, raw_cell)
+                    self.execution_count += 1
+                    
+                    return
             
             # Store raw and processed history
             if store_history:

IPython/core/tests/test_interactiveshell.py

@@ -91,3 +91,9 b' class InteractiveShellTestCase(unittest.TestCase):'
         ip = get_ipython()
         ip.run_cell('a = """\n%exit\n"""')
         self.assertEquals(ip.user_ns['a'], '\n%exit\n')
+    
+    def test_alias_crash(self):
+        """Errors in prefilter can't crash IPython"""
+        ip = get_ipython()
+        ip.run_cell('%alias parts echo first %s second %s')
+        ip.run_cell('parts 1')