Changing sh-mode shell type.

[Oleksandr Gavenko <gavenko@bifit.com.ua>]

According to 'sh-mode':

   If you generally program a shell different from your login shell
   you can set `sh-shell-file' accordingly.

As usual I try add:

   # -*- sh-shell-file: "/bin/zsh"; mode: sh -*-

but it set to "bash" in any case...

I debug issue and found that when you enter into
'sh-mode' function 'sh-shell-file' have value "/bin/bash"
as it set by:

   (defcustom sh-shell-file ...)

so executed:

   (sh-set-shell
    (cond ((save-excursion
         ....  ....
          (t
           sh-shell-file))
     nil nil)

It is possible pass file local variable before mode activation
code was executed??