Dynamic variable for scoped guard fail handler function.

Generates a diction validation guard function calling function `f` with
variadic arguments given a diction `element-id` successful validation and
calling the atom function variable `guard-fail-f` if validation fails.
The optional `v-extract-f` is used to extract the value to be validated
against the `element-id` from the `args` vector; defaults to `first`.

Atom with guard fail function.

Sets the guard fail function atom `guard-fail-f` to `f`.
The `guard-fail-f` has a signature [element-id guarded-f arg-value-validated
extract-arg-f failures & args].