Consider adding warning for advanced indexing with logical indexer

[wbernoudy]

Currently, we don't support boolean indexing in our implementation of advanced indexing (AdvancedIndexingNode).

If an ArrayNode which is logical is used to index another node, AdvancedIndexingNode will simply treat it as any other integer indexer, and return a selection of the first and second elements of the main array. Though this is technically correct, it is somewhat of a departure from the numpy behavior.

To help clarify this to users, we could raise a warning if the indexer is logical to say that it will be treated as an integer index.