Set exit code on script errors. Only handle the issue related to .py scripts. 1. interactiveshell: The method safe_execfile is not totally safe now. Errors of user scripts are raised to a higher level, where we can decide what to do. 2. execution: The %run magic catches exceptions from safe_execfile. 3. shellapp: The _run_cmd_line_code method catches exceptions from safe_execfile and sets the right exit status. Partial-revert: 1. Change execution.py back. 2. Revert some changes in safe_execfile, then modify the excetion handling logic.