Represent 'unit' as C 'int'; change pattern match compilation to avoid 'goto'; change Postgres prepared statement compilation to make life easier for the GCC escape analysis; all this in support of better tail call optimization

signature S = sig
        type t
        val x : t
end

signature S' = sig
        include S
        val y : t
end

signature S'' = sig
        type u
        include S' where type t = int
        type v
end