ImageCache improvement: Better behavior when multiple threads all need the same tile simultaneously and it's not in cache (so they will all ready and try to add it separately).  Instead of "last one to add wins", change to "first one to add wins", which cuts memory use by keeping multiple copies of the same tile from ending up in the microcaches of several threads.
ImageCache improvement: Better behavior when multiple threads all need
the same tile simultaneously and it's not in cache (so they will all
ready and try to add it separately).  Instead of "last one to add wins",
change to "first one to add wins", which cuts memory use by keeping
multiple copies of the same tile from ending up in the microcaches of
several threads.


git-svn-id: c3edda122e248ef33995da003806c930f62b9468@1288 31904243-a364-42ac-a3db-9305396518ba

cwilling/oiio,YangYangTL/oiio,lgritz/oiio,cwilling/oiio,OpenImageIO/oiio,bdeluca/oiio,scott-wilson/oiio,micler/oiio,lgritz/oiio,YangYangTL/oiio,mcanthony/oiio,OpenImageIO/oiio,mcanthony/oiio,cwilling/oiio,scott-wilson/oiio,bdeluca/oiio,scott-wilson/oiio,cwilling/oiio,micler/oiio,bdeluca/oiio,scott-wilson/oiio,micler/oiio,OpenImageIO/oiio,jeremyselan/oiio,jeremyselan/oiio,sambler/oiio,jeremyselan/oiio,YangYangTL/oiio,sambler/oiio,OpenImageIO/oiio,sambler/oiio,YangYangTL/oiio,lgritz/oiio,mcanthony/oiio,micler/oiio,mcanthony/oiio,sambler/oiio,lgritz/oiio,bdeluca/oiio