bug#24982: 24.5; way to let Elisp reader ignore unreadable #(...) constructs

[Drew Adams]

> The problem is when the thing inside the construct is unreadable, not
> when there's errors (in a syntactically valid form).  For instance:
> 
> (ignore-errors #0)
> 
> In Common Lisp, this is the #| ...  |# operator, and it's handy
> occasionally.  It's really like a nesting comment thing...

Good point.  I was thinking of #(...), but yes,
the situation is more general.  It's about #
syntax that's found to be invalid, but for cases
where # nevertheless can tell where the sexp
parsing should end (and so can advance point there).