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/throwoutside.c

@@ -5,11 +5,15 @@ int main(void)
   TRY {
     TRY {
       THROW(3, NULL);
+    } EXCEPT {
     } CATCH(5) {
       EXCLIB_TRACE("Caught 5");
+    } FINALLY {
     } ETRY;
+  } EXCEPT {
   } CATCH(3) {
     EXCLIB_TRACE("Caught 3");
+  } FINALLY {
   } ETRY;
 
   return 0;