org-compat: Add kludges for time-related functions

* lisp/org-compat.el (org-decode-time, org-format-time-string)
(org-time-add, org-time-less-p, org-time-since, org-time-subtract):
New compatibility functions.

On Emacs 24, these functions are stricter about what they accept for
time.  These new function will be used to port over changes in the
Emacs repo.  Don't bother doing a bulk substitution in existing Org
code because that would produce a lot of churn and these calls should
already be compatible with Emacs 24.

lisp/org-compat.el

@@ -157,6 +157,35 @@ This is a floating point number if the size is too large for an integer."
 Case is significant."
     (string< s1 s2)))
 
+;; The time- functions below translate nil to `current-time` and
+;; accept an integer as of Emacs 25.  `decode-time` and
+;; `format-time-string` accept nil on Emacs 24 but don't accept an
+;; integer until Emacs 25.
+(if (< emacs-major-version 25)
+    (let ((convert
+           (lambda (time)
+             (cond ((not time) (current-time))
+                   ((numberp time) (seconds-to-time time))
+                   (t time)))))
+      (defun org-decode-time (&optional time)
+        (decode-time (funcall convert time)))
+      (defun org-format-time-string (format-string &optional time universal)
+        (format-time-string format-string (funcall convert time) universal))
+      (defun org-time-add (a b)
+        (time-add (funcall convert a) (funcall convert b)))
+      (defun org-time-subtract (a b)
+        (time-subtract (funcall convert a) (funcall convert b)))
+      (defun org-time-since (time)
+        (time-since (funcall convert time)))
+      (defun org-time-less-p (t1 t2)
+        (time-less-p (funcall convert t1) (funcall convert t2))))
+  (defalias 'org-decode-time 'decode-time)
+  (defalias 'org-format-time-string 'format-time-string)
+  (defalias 'org-time-add 'time-add)
+  (defalias 'org-time-subtract 'time-subtract)
+  (defalias 'org-time-since 'time-since)
+  (defalias 'org-time-less-p 'time-less-p))
+
 
 ;;; Obsolete aliases (remove them after the next major release).