If the image has the id IMAGEID, then we use the id ref_IMAGEID
for the figure number. Closes#7551.
This allows one to create a filter that adds a figure number
with figure name, e.g.
<w:fldSimple w:instr=" REF ref_superfig "><w:r><w:t>Figure X</w:t></w:r></w:fldSimple>
For this to be possible it must be possible to predict the
figure number id from the image id.
If images lack an id, an id of the form `ref_fig1` is used.
John MacFarlane
6271b09c50