Make Org future-proof

* lisp/org.el (org-small-year-to-year): Do not hardcode 2037 as the
  last future year for Org.  Always foresee the next 30 years.

lisp/org.el

@@ -17456,14 +17456,15 @@ The variable `date' is bound by the calendar when this is called."
 
 (defun org-small-year-to-year (year)
   "Convert 2-digit years into 4-digit years.
-38-99 are mapped into 1938-1999.  1-37 are mapped into 2001-2037.
-The year 2000 cannot be abbreviated.  Any year larger than 99
-is returned unchanged."
-  (if (< year 38)
-      (setq year (+ 2000 year))
-    (if (< year 100)
-	(setq year (+ 1900 year))))
-  year)
+YEAR is expanded into one of the 30 next years, if possible, or
+into a past one.  Any year larger than 99 is returned unchanged."
+  (if (>= year 100) year
+    (let* ((current (string-to-number (format-time-string "%Y" (current-time))))
+	   (century (/ current 100))
+	   (offset (- year (% current 100))))
+      (cond ((> offset 30) (+ (* (1- century) 100) year))
+	    ((> offset -70) (+ (* century 100) year))
+	    (t (+ (* (1+ century) 100) year))))))
 
 (defun org-time-from-absolute (d)
   "Return the time corresponding to date D.