Update: get only exist status when processing return, use "return_code", and set...

Update: get only exist status when processing return, use "return_code", and set return error manually where applicable.

The return code also stores signal information.
To properly return the expected return code, WEXITSTATUS() should be used.

In some cases a return code of "0" is always returned, even on error.
In these cases, now return "1" if an error is detected.

Use "return_code" more consistently, it is more explicit than "result" or "results".