A fix for show-paren-function problem

[Richard . G . Bielawski]

I believe the following patch to show-paren-function in paren.el
will fix a long standing bug that causes show-paren-mode to
incorrectly highlight matching parens as mismatched if their
syntax was assigned via font-lock-syntactic-keywords or put.

The patch does not change the current behavior in text where 
syntax is determined by the syntax table alone.  But it does 
afford the programmer assigning syntax arbitrarily more 
flexibility in determining what will be considered a match.

For example:
All these pairs should highlight as properly matched:
Begin End     begin end       BEGIN END    begin end;
^       ^     ^       ^       ^       ^    ^        ^
While these are mismatched because `block' requires `end block'.
block end;
^       ^
Such conditions are easily handled by the fix below while
not changing purely syntax-table based matching in any way.

   ;; If found a "matching" paren, see if it is the right
   ;; kind of paren to match the one we started at.
   (when (integerp pos)
     (let ((beg (min pos oldpos)) (end (max pos oldpos)))
       (when (/= (char-syntax (char-after beg)) ?\$)
         (setq mismatch
-              (not (eq (char-before end)
+              (not (eq (or (cdr (get-text-property (1- end) 'syntax-table))
+                           (char-before end))
                        ;; This can give nil.
-                       (matching-paren (char-after beg)))))))))))
+                       (or (cdr (get-text-property beg 'syntax-table))
+                           (matching-paren (char-after beg))))))))))))


Richard Bielawski