Description:
------------
It would be nice to have an optional function handler for when set_time_limit() goes over the set amount of time.

Reproduce code:
---------------
<?

   set_time_limit(30, "errfunc");
   while(1) { $g=1; }

   function errfunc()
   {
      echo "Hey, this is taking too long!";
      exit;
   }
?>

Expected result:
----------------
After 30 seconds, errfunc() is called, and the program executes gracefully, without an error message and a line number.

This would be useful, say, if doing a merchant transaction with a separate server and it's stalling on giving a response.

Actual result:
--------------
Hey, this is taking too long