get_value_box duplication

[jbrockmendel]

tslib.get_value_box seems out of place. The only place it is used is in base.index. Meanwhile _libs.index.get_value_at looks very similar but is never used. (It also looks similar to a chunk of code in IndexEngine.get_value

Is it possible that index.get_value_at was intended to replace tslib.get_value_box?

[gfyoung]

@jbrockmendel : Have a look at the blame tab on GitHub for this file. That might be of use, though other maintainers probably know better than I here.