(sh-shells): Eliminated variable redundant with

(sh-shells): Eliminated variable redundant with
`interpreter-mode-alist'.
(sh-beginning-of-command): Take into account \quoted newline.
(sh-builtins, sh-leading-keywords, sh-other-keywords): Now three
distinct sets for font-locking.
(sh-font-lock-keywords-1, sh-font-lock-keywords-2): New variables
and functions to give the user finer control over how much to fontify,
including new distinction between keywords and builtins.
(sh-mode): Use new features of `font-lock-defaults' and adaptation
to skeleton changes.
(sh-while): Fix csh, es & rc skeletons.