Use completion-in-buffer and remove uses of dynamic scoping.

Use completion-in-buffer and remove uses of dynamic scoping.
* progmodes/pascal.el (pascal-str, pascal-all, pascal-pred)
(pascal-buffer-to-use, pascal-flag): Don't declare.
(pascal-func-completion, pascal-type-completion, pascal-var-completion)
(pascal-get-completion-decl, pascal-keyword-completion):
Add `pascal-str' argument, save-excursion,
return the found completions, and don't filter with pascal-pred.
(pascal-completion-cache): New var.
(pascal-completion): Don't switch buffer any more (it was never
necessary).  Don't save-excursion any more (it's done by the called
subroutines).  Use a cache to avoid redundant computations.
Use complete-with-action rather than pascal-completion-response and
let it apply the predicate as well.
(pascal-complete-word): Use completion-in-buffer when
pascal-toggle-completions is nil.
(pascal-show-completions): Don't bind pascal-buffer-to-use since it's
not used any more.
(pascal-comp-defun): Don't change buffer any more.
Use complete-with-action rather than pascal-completion-response and
let it apply the predicate as well.
(pascal-goto-defun): Change buffer before calling pascal-comp-defun
when neded.