[O] Bug and possible fix / work-around using org-mobile with group tags

[John Hutchinson]

1. Running org-mobile-push with group tags defined in init.el file using :startgrouptag etc. results in an error, and (in my case) DropBox not being updated. Here's the log from the *Messages* buffer:

   Creating agendas...
   Agenda written to Org file /cygdrive/c/Users/IBM_ADMIN/Dropbox/Apps/MobileOrg/agendas.org
   Creating agendas...done
   Saving all Org-mode buffers...
   (No files need saving)
   Saving all Org-mode buffers... done
   Copying files...
   Writing index file...
   org-mobile-create-index-file: Wrong type argument: sequencep, :startgrouptag
   Quit
    [2 times]
   

2. Commenting out the group tags attributes in init.el results in Org Mobile successfully generating and pushing to DropBox.
3. Turning group tags off with org-toggle-tags-groups and running org-mobile-push causes the error.
4. Using Org from org-plus-contrib-20160208, the problem seems to be the :startgroup and :endgroup on lines 460 and 461 of org-mobile.el; patching them to :startgrouptag and :endgrouptag respectively appears to correct the issue (though I've not done in-depth testing for any other unintended side effects this patch may have).
5. Also, changing the group attributes in my init.el from :startgrouptag :endgrouptag to :startgroup and :endgroup respectively corrects the issue, although the Org manual indicates that the longer form is correct.
   
6. As an aside, I note there are several instances of plain :startgroup intermingled with :startgrouptag in the org sources:

   org-plus-contrib-20160208 $ grep -n startgroup *.el
   org.el:3492:		 (const :startgroup)
   org.el:3495:		 (const :startgrouptag)
   org.el:3523:	   (const :tag "Start radio group" (:startgroup))
   org.el:5063:				   (append '((:startgroup))
   org.el:5233:		      (:startgroup "{")
   org.el:5235:		      (:startgrouptag "[")
   org.el:5252:	  (push '(:startgroup) org-tag-alist)
   org.el:5258:	  (push '(:startgrouptag) org-tag-alist)
   org.el:5322:      (if (or (memq (car e) '(:newline :grouptags :endgroup :startgroup))
   org.el:13093:	   ((equal e '(:startgroup))
   org.el:15232:	 ((eq (car e) :startgroup)
   org.el:15241:	 ((eq (car e) :startgrouptag)
   org-interactive-query.el:92:	 ((equal e '(:startgroup))
   org-interactive-query.el:268:     ;; if this is not a keyword (:startgroup, etc), ignore it
   org-mobile.el:460:			      ((eq (car x) :startgroup) "{")
   org-pcomplete.el:245:		  ((eq :startgroup (car x)) "{")
   ox-beamer.el:1128:	  (append '((:startgroup))
   

Regards,

=John

P.S. First time writing to this list; apologies in advance for breaches of etiquette.