Added a CLEANUP mechanism to the exception handling library. Fixed a bug in the way setjmp() return codes were being handled that lead to infinite loops in some cases, exceptions getting missed in others. Made FINALLY {} a required element (unfortunately).

demo/finally.c

@@ -5,8 +5,9 @@ int main(void)
 {
   TRY {
     THROW(2, NULL);
+  } EXCEPT {
   } FINALLY {
-    printf("I am in the finally clause, and I am about to issue an unhandled exception error.\n");
+      printf("I am in the finally clause, and I am about to issue an unhandled exception error.\n");
   } ETRY;
   return 0;
 }