Mere use of `fast_pointer_cast` does not imply the availability of a blind cast

This is necessary to keep object file sizes to a managable level.  Registries like this one can wind up costing a lot of object space.  This adjustment by itself results in a 3MB object file size difference in AutoFilterTest.
Merge pull request #310 from leapmotion/ref-blindcast

Mere use of `fast_pointer_cast` does not imply the availability of a blind cast