* lisp/org-icalendar.el (org-print-icalendar-entries): Add 'uid text

  property based on the ID property of the org entry to the first
  character of the diary entry.

This text property can be used by `icalendar--create-uid', instead
of creating a uid by itself.

NOTE: `icalendar--create-uid' should be patched to pick up this uid.

TINYCHANGE

lisp/org-icalendar.el

@@ -432,7 +432,10 @@ When COMBINE is non nil, add the category to each line."
 	  (if scheduledp (setq summary (concat "S: " summary)))
 	  (if (string-match "\\`<%%" ts)
 	      (with-current-buffer sexp-buffer
-		(insert (substring ts 1 -1) " " summary "\n"))
+		(let ((entry (substring ts 1 -1)))
+		  (put-text-property 0 1 'uid
+				     (concat " " prefix uid) entry)
+		  (insert entry " " summary "\n")))
 	    (princ (format "BEGIN:VEVENT
 UID: %s
 %s