Export backends: Interpret correctly DATE keyword

* contrib/lisp/org-e-ascii.el (org-e-ascii-template--document-title):
  Interpret correctly DATE keyword.
* contrib/lisp/org-e-html.el (org-e-html-format-date): Interpret
  correctly DATE keyword.
* contrib/lisp/org-e-latex.el (org-e-latex-template): Interpret
  correctly DATE keyword.
* contrib/lisp/org-e-odt.el (org-e-odt-format-preamble,
  org-e-odt-update-meta-file): Interpret correctly DATE keyword.

contrib/lisp/org-e-ascii.el

@@ -901,7 +901,7 @@ INFO is a plist used as a communication channel."
 		       (and auth (org-export-data auth info)))))
 	(email (and (plist-get info :with-email)
 		    (org-export-data (plist-get info :email) info)))
-	(date (plist-get info :date)))
+	(date (org-export-data (plist-get info :date) info)))
     ;; There are two types of title blocks depending on the presence
     ;; of a title to display.
     (if (string= title "")

contrib/lisp/org-e-html.el

@@ -1407,7 +1407,7 @@ Replaces invalid characters with \"_\"."
 	(mapconcat 'org-e-html-format-footnote-definition fn-alist "\n"))))))
 
 (defun org-e-html-format-date (info)
-  (let ((date (plist-get info :date)))
+  (let ((date (org-export-data (plist-get info :date) info)))
     (cond
      ((and date (string-match "%" date))
       (format-time-string date))

contrib/lisp/org-e-latex.el

@@ -1084,7 +1084,7 @@ holding export options."
 	     (author (format "\\author{%s}\n" author))
 	     (t "\\author{}\n")))
      ;; 6. Date.
-     (let ((date (plist-get info :date)))
+     (let ((date (org-export-data (plist-get info :date) info)))
        (and date (format "\\date{%s}\n" date)))
      ;; 7. Title
      (format "\\title{%s}\n" title)

contrib/lisp/org-e-odt.el

@@ -124,7 +124,7 @@ structure of the values.")
 	 (author (and (plist-get info :with-author)
 		      (let ((auth (plist-get info :author)))
 			(and auth (org-export-data auth info)))))
-	 (date (plist-get info :date))
+	 (date (org-export-data (plist-get info :date) info))
 	 (iso-date (org-e-odt-format-date date))
 	 (date (org-e-odt-format-date date "%d %b %Y"))
 	 (email (plist-get info :email))
@@ -1066,7 +1066,8 @@ ATTR is a string of other attributes of the a element."
   (let ((title (org-export-data (plist-get info :title) info))
 	(author (or (let ((auth (plist-get info :author)))
 		      (and auth (org-export-data auth info))) ""))
-	(date (org-e-odt-format-date (plist-get info :date)))
+	(date (org-e-odt-format-date
+	       (org-export-data (plist-get info :date) info)))
 	(email (plist-get info :email))
 	(keywords (plist-get info :keywords))
 	(description (plist-get info :description)))