[[ Bug 20431 ]] Show ask/answer dialogs in correct location on Mac

This patch fixes an issue on Mac where if the screenRect has a non-0
top then the dialogs won't be shown at the correct location. The patch
is the same to both stacks:

```
 switch the platform
       case "MacOS"
          local tMacOSX
          put true into tMacOSX
          set the loc of this stack to tStackLoc
-         set the top of this stack to round(item 4 of tScreenRect/5)
+         set the top of this stack to item 2 of tScreenRect + round(tScreenHeight/5)
```

Author: montegoulding

Toolset/palettes/revanswerdialog.rev

@@ -0,0 +1 @@
+# Show ask and answer dialogs in correct location when the screen top is not 0