Fix compiler warnings related to array_view
Fix compiler warnings related to array_view

* array_view::size() must be constexpr only when bounds.size() is (C++14 only)
* Give explicit namespace for OIIO::bounds class type so it doesn't clash
  with the name for array_view::bound() method.

lgritz/oiio,YangYangTL/oiio,lgritz/oiio,lgritz/oiio,YangYangTL/oiio,lgritz/oiio,bdeluca/oiio,OpenImageIO/oiio,OpenImageIO/oiio,bdeluca/oiio,YangYangTL/oiio,YangYangTL/oiio,micler/oiio,micler/oiio,bdeluca/oiio,micler/oiio,bdeluca/oiio,OpenImageIO/oiio,micler/oiio,OpenImageIO/oiio