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.

testcode/lib/atari/defdev.c

@@ -13,6 +13,6 @@ extern char _defdev[];
 int main(void)
 {
         printf("default device: %s\n", _defdev);
-        if (! _is_cmdline_dos()) cgetc();
+        if (doesclrscrafterexit()) cgetc();
         return 0;
 }

testcode/lib/atari/mem.c

@@ -41,6 +41,6 @@ int main(void)
   printf("  sp:              $%04X  (stack ptr)\n", getsp());
 
   if (allocmem) free(allocmem);
-  if (! _is_cmdline_dos()) cgetc();
+  if (doesclrscrafterexit()) cgetc();
   return(0);
 }