avoid repeatedly setting repub state to be 3

There are reports that the microfilm republishing software is repeatedly setting the repub state of an item to be 3 (even when it is already set), through modify_xml tasks.

I understand from Hank that this may be from the unanticipated use case of checking something in several times before actually deriving it.

So we need to confirm this (that this pathway is possible), and, if so, put in some check like grabbing the itemxml and then not setting repub state to 3 if it is already 3 (or, in fact, setting any metadata to values which they already carry).