[Orgmode] Install warning for org-7 for forgetful users

[Robert Horn]

I ran into this, so I'll warn others.  It might belong in the notes for
org-7.01.

If you have a newer version of emacs that has org already integrated,
you get some, but not all, of the org-7.01 features functioning if you
have org-7.01 set as the auto-load directory.  I had been using org by
having the lines:

(setq load-path (cons "~/org-6.xxx/lisp" load-path))
(require 'org-install)

in my .emacs.  I forgot that I had upgraded emacs and org was now
integrated into emacs. I just changed org-6.xxx to org-7.01g to try out
the new version.  Odd things resulted.  It actually worked well enough
to do some work, but then I found occasional stuff that did not work.  I
used the brute force fix of just moving all the org-* files into a
temporary directory, thus slowing down the startup but ensuring that I
could test the new version without having headaches if I wanted to revert.

There might be a better method than this.  It's probably worth
mentioning in the release notes.