Alternate guard form - evaluate the guard clauses in the continuation of the raise.
We need to override the current-exception-handler and still pass a thunk to be
applied on return, but this allows us to print stack traces inside guards.
checking for NULLs before checking exceptions
Initialize record fields to void.
Adding an explicit error for record rtd and constructor conflicts.
Using cond-expand for faster match-check-ellipsis and match-check-identifier in Chibi.