New compatibility macro `org-with-silent-modifications'

New compatibility macro `org-with-silent-modifications'

* org-macs.el: Don't define `with-silent-modifications' for
emacsen that don't have it.

* org-compat.el (org-with-silent-modifications): New
compatibility macro.

* org.el (org-refresh-category-properties)
(org-refresh-properties, org-entry-blocked-p)
(org-agenda-prepare-buffers):
* org-indent.el (org-indent-remove-properties)
(org-indent-add-properties):
* org-colview.el (org-columns-display-here)
(org-columns-remove-overlays, org-columns-quit)
(org-columns-edit-value, org-columns-compute-all)
(org-columns-compute, org-agenda-colview-compute):
* org-clock.el (org-clock-sum): Use the compatibility macro
`org-with-silent-modifications' instead of
`with-silent-modifications'.

Thanks to Achim for a preliminary patch.