Function returning MRS values should explicitly return them

Good:

```igorpro
Function [variable ret, string msg] DoSomething()

	return [4711, "some text"
End

Function [variable ret, string msg] DoSomething()

    ret = 4711
    msg = "some text"
	return [ret, msg]
End
```

Bad:

```igorpro
Function [variable ret, string msg] DoSomething()

    ret = 4711
    msg = "some text"
    // missing return statement
End
```