Cover letfn bindings. Massive duplication between wrap-letfn-binding and wrap-function-overload (and for the plural versions) but it works.
Pull wrap-fn-bindings out of wrap-overloads and wrap-letfn-bindings
Oops. Mildly incorrect Extract Method refactoring.
Remove a fixed FIXME
Merge pull request #19 from frankshearar/support-letfn

doesn't recognize letfn/letfn*