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/helpers.c

@@ -4,10 +4,13 @@ int main(void)
 {
   TRY {
     THROW_ZERO(NULL, EXC_NULLPOINTER, "I just threw with THROW_ZERO");
+  } CLEANUP {
+  } EXCEPT {
   } CATCH ( EXC_NULLPOINTER ) {
     THROW_NONZERO(strcmp("not", "equal"),
 		  3,
 		  "strcmp was nonzero!");
+  } FINALLY {
   } ETRY;
 
   return 0;