Port `examples`, `interactions`, etc., to use the new `examples`
form of `scribble/examples`. The main intended effect is to ensure
that errors are produced by examples only as specifically
indicated.
Nested splicing forms would lead to an "ambigious binding" error
when the nested forms bind the same name, such as in
(splicing-let ([a 1])
(splicing-let ([a 2])
(define x a)))
The problem is that splicing is implemented by adding a scope to
everything in the form's body, but removing it back off the
identifiers of a definition (so the `x` above ends up with no new
scopes). Meanwhile, a splicing form expands to a set of definitions,
where the locally bound identifier keeps the extra scope (unlike
definitions from the body). A local identifier for a nested splicing
form would then keep the inner scope but lose the outer scope, while
a local identifier from the outer splicing form would keep the outer
scope but no have the inner one --- leading to ambiguity.
The solution in this commit is to annotate a local identifier for a
splicing form with a property that says "intended to be local", so the
nested definition will keep the scope for the outer splicing form as
well as the inner one. It's not clear that this is the right approach,
but it's the best idea I have for now.
