Added more tag testing in IECore LinkedSceneTest which shows a bug in readTags/hasTag.
Added more tag testing in IECore LinkedSceneTest which shows a bug in readTags/hasTag.

danieldresser/cortex,appleseedhq/cortex,hradec/cortex,goddardl/cortex,danieldresser/cortex,davidsminor/cortex,appleseedhq/cortex,davidsminor/cortex,appleseedhq/cortex,davidsminor/cortex,hradec/cortex,lento/cortex,lento/cortex,goddardl/cortex,davidsminor/cortex,danieldresser/cortex,goddardl/cortex,danieldresser/cortex,lento/cortex,hradec/cortex