1) avoid stale data 2) fix backspace issue

1) avoid stale data 2) fix backspace issue

more specifically:
    1 - if a response from the server is not the response to the most
        recent request issued by the AutoSuggestStore, don't use it
    2 - when the search query is empty, empty the store (previously we
        knew not to talk to the server but didn't empty the store)

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>