[Orgmode] org-5.15 & emacs 21 compatibility: time-date.el version issue

[Eric J Haywiser]

Dear orgers,

Sometime between org-5.10 and org-5.15 the agenda command C-a a began 
initiatating a call to a new command time-subtract.

Unfortunately, time-subtract is not present in the time-date.el
that is shipped with some emacs 21.

In the older date-time.el subtract-time is provided instead.

Adding the following to ones startup under emacs 21 seems resolve this:

(load-library "time-date")
(if (not(fboundp 'time-subtract))
    (defalias 'time-subtract 'subtract-time)
  )

Would distributing such tweaks/backports in an emacs21
subdir of org much like the xemacs tweaks be appropriate?