i.e. revert

commit 162c72d6
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Fri Jan 23 13:17:39 2015 +0000

and

commit ad50b9a8
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Fri Jan 23 15:52:58 2015 +0000

    Related: fdo#78599 wrong method

and restore the original RegisterToFormat logic, and
instead block setting modifications of the document
until the explicit SetModified call to avoid the
original problem of trying to generate a preview
of the document during the section where it cannot be
done

Change-Id: I9dbec0a371d4d747b780aa271789d50a46eccefd
Reviewed-on: https://gerrit.libreoffice.org/31917Reviewed-by: Justin Luth <justin_luth@sil.org>
Tested-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>