fixed compilation error on Windows: missing definition of PTEX_EXPORTS caused dll import/export error
fixed compilation error on Windows: missing definition of PTEX_EXPORTS caused dll import/export error

git-svn-id: c3edda122e248ef33995da003806c930f62b9468@1748 31904243-a364-42ac-a3db-9305396518ba

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