org-agenda: Write only currently visible items

* lisp/org-agenda.el (org-agenda-write): Fix arguments passed to
  `org-agenda-remove-marked-text' to properly remove entries with
  `invisible' property set to `org-filtered'.
* lisp/ox-icalendar.el (org-icalendar-export-current-agenda): Always
  include TODO entries in the output.  The motivation is that a user not
  filtering out TODO or DONE items in the current agenda probably wants
  them in the output.

Reported-by: "sgeorgii ." <sgeorgii@gmail.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/102998>

lisp/org-agenda.el

@@ -3349,7 +3349,7 @@ the agenda to write."
 	     (rename-buffer org-agenda-write-buffer-name t)
 	     (set-buffer-modified-p nil)
 	     (insert bs)
-	     (org-agenda-remove-marked-text 'org-filtered)
+	     (org-agenda-remove-marked-text 'invisible 'org-filtered)
 	     (run-hooks 'org-agenda-before-write-hook)
 	     (cond
 	      ((org-bound-and-true-p org-mobile-creating-agendas)

lisp/ox-icalendar.el

@@ -901,7 +901,9 @@ This function assumes major mode for current buffer is
 			    (buffer-substring
 			     (point) (progn (outline-next-heading) (point)))))))))
 		   (forward-line)))))
-	   'icalendar t '(:ascii-charset utf-8 :ascii-links-to-notes nil))))
+	   'icalendar t
+	   '(:ascii-charset utf-8 :ascii-links-to-notes nil
+			    :icalendar-include-todo all))))
     (with-temp-file file
       (insert
        (org-icalendar--vcalendar