lisp/org-agenda.el: Make tags filtering case-sensitive

* lisp/org-agenda.el (org-agenda-filter)
(org-agenda-get-represented-tags)
(org-agenda-filter-make-matcher-tag-exp): Make tags filtering
case-sensitive.

This fixes a bug introduced in commit 13a1a4fb9.

lisp/org-agenda.el

@@ -7761,8 +7761,8 @@ the variable `org-agenda-auto-exclude-function'."
 	  (setq s (replace-regexp-in-string ; Remove the temporary special string.
 		   "~~~" "-" (match-string 3 f-string)))
 	  (cond
-	   ((member (downcase s) tag-list)
-	    (add-to-list 'ft (concat pm (downcase s)) 'append 'equal))
+	   ((member s tag-list)
+	    (add-to-list 'ft (concat pm s) 'append 'equal))
 	   ((member s category-list)
 	    (add-to-list 'fc (concat pm ; Remove temporary double quotes.
 				     (replace-regexp-in-string "\"\\(.*\\)\"" "\\1" s))
@@ -7962,8 +7962,8 @@ These will be lower-case, for filtering."
 	  (dolist (tag tags-lists)
 	    (mapc
 	     (lambda (group)
-	       (when (member tag (mapcar #'downcase group))
-		 (push (downcase (car group)) tags-lists)))
+	       (when (member tag group)
+		 (push (car group) tags-lists)))
 	     org-tag-groups-alist-for-agenda))
 	  (setq org-agenda-represented-tags tags-lists)))))
 
@@ -8037,7 +8037,7 @@ function to set the right switches in the returned form."
 		 ((and (string-match-p "\\`{" tag) (string-match-p "}\\'" tag))
 		  ;; TAG is a regexp.
 		  (list 'org-match-any-p (substring tag 1 -1) 'tags))
-		 (t (list 'member (downcase tag) 'tags)))))
+		 (t (list 'member tag 'tags)))))
 	(push (if (eq op ?-) (list 'not f) f) form)))))
 
 (defun org-agenda-filter-effort-form (e)