Doc fixes.

Doc fixes.
(customize-set-variable, customize-save-variable): Rename args for
doc.
(custom-variable-tag-face, custom-face-tag-face)
(custom-group-tag-face-1, custom-group-tag-face): Modify from
style which user identify as hyperlink.
(hook): Don't add undefined functions to the hook.
(debug-ignored-errors): Transfer message from bindings.el.