When an invalidate_all occurs, make sure the purge of per-thread caches not only have their tile micro-cache cleared, but also the file pointer microcache zeroed out.
When an invalidate_all occurs, make sure the purge of per-thread caches
not only have their tile micro-cache cleared, but also the file pointer
microcache zeroed out.

This was leading to a cascade of errors and a crash in the following sequence:
   1. ask for texture from a file that doesn't exist
   2. invalidate_all
   3. ask for texture again from the same file (that still doesn't exist)



git-svn-id: c3edda122e248ef33995da003806c930f62b9468@1338 31904243-a364-42ac-a3db-9305396518ba

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