This is a bit more standard, and has the bonus of being compatible with Devise, which is using `flash[:notice]` and so its flashes were coming out unstyled, oops!
In particular, outfit_id == 0 would cause outfit_id? to
return false, so it wouldn't run the outfit presence
validation, so /donations/features would try to load
outfit #0 and fail.
Also, flash[:alert] instead of flash[:error] when outfit_id
is bad.
