Don't quit the interactive loop when Ctrl-C is pressed.

NOTE: this doesn't address issue #36, which happens when you start say
'cat' and Ctrl-C.  The Python interpreter still gets the signal then.

bin/oil.py

@@ -109,11 +109,7 @@ def InteractiveLoop(opts, ex, c_parser, arena):
      w = c_parser.Peek()
    except KeyboardInterrupt:
      print('Ctrl-C')
      break

    # TODO: When does this happen?
    if w is None:
      raise RuntimeError('Failed parse: %s' % c_parser.Error())
      continue

    c_id = word.CommandId(w)
    if c_id == Id.Op_Newline: