(sh-font-lock-keywords-var): Variable renamed from sh-font-lock-keywords.

(sh-font-lock-keywords-var): Variable renamed from sh-font-lock-keywords.
In the `shell' entry, don't try to refer to executable-font-lock-keywords.
(sh-font-lock-keywords-var-1): Renamed from sh-font-lock-keywords-1.
(sh-font-lock-keywords-var-2): Renamed from sh-font-lock-keywords-2.
(sh-font-lock-keywords): Append executable-font-lock-keywords here.
(sh-mode): Set comment-start-skip, local-abbrev-table, imenu-case-fold-search.
(sh-set-shell): Don't set them here.
(sh-feature): Simplify.  Get rid of the eval-a-variable feature.
Don't cache the results in the original alist; don't ever modify that alist.