Scheme mode syntax fixes

[Dave Love]

The syntax of `|' in Scheme mode should be "\" 23" to account for
symbol-quoting, e.g. `|foo bar|'.  Also `#' should have syntax "' 14n"
for nestable inline comments, and should be taken out of the font-lock
syntax alist in font-lock-defaults.  (These aren't R5RS syntax, but
are supported by some current implementations.)

Then I think `lisp-font-lock-syntactic-face-function' should avoid
fontifying the quoted symbols as strings.  The `font-lock-string-face'
at the end should be replaced by something like

(if (eq ?| (nth 3 state))
    nil
  font-lock-string-face)

This will apply to, and be appropriate for, Common Lisp too.