Add Atari version of of doesclrscrafterexit().

- Update documentation.
- Update atari.h and apple2.h header files.
- Adapt Atari test/target programs.
- Fix a typo in "div" entry in funcref.sgml.

libsrc/atari/targetutil/w2cas.c

@@ -35,7 +35,7 @@ static struct __iocb *findfreeiocb(void)
 static void exitfn(void)
 {
     /* if DOS will automatically clear the screen, after the program exits, wait for a keypress... */
-    if (! _is_cmdline_dos())
+    if (doesclrscrafterexit())
         cgetc();
 }