`org-id-update-id-locations' should also scan the files listed in `org-id-locations-file'

[laslydone]

Since you can add to `org-id-locations-file' without having to put the
files in `org-id-locations' I think it would make more sense to also
scan `org-id-locations-file'.

Currently you can empty `org-id-locations-file' (".org-id-locations"):
  1. $ emacs -Q <RET>
  2. C-x C-f ztest.org <RET>
  3. C-RET heading <RET>
  4. M-x org-id-get-create <RET>
  5. C-x C-s
  6. C-x C-c
  7. $ emacs -Q <RET>
  8. C-x C-f ztest.org <RET>
  9. M-x org-id-update-id-locations <RET>
  10. C-x C-c