Allow idle display after the buffer is saved.

[leungbk]

Because the buffer is saved after Dante performs checks, the save confirmation appearing in the echo area can prevent the idle-induced type display from appearing. It's also possible for many requests to pile up if the idle-display threshold is set low, so the last valid idle type display is saved as a temp variable.

I'm not catching every failure case--sometimes haskell-doc.el will have its own type annotation already in the echo area and Dante will respect it; and shortly after startup, sometimes stuff won't idly display. I'm not sure how to resolve these cases, but this patch covers at least many of the other scenarios.

[leungbk]

Friendly ping @jyp.

[jyp]

Thanks, sorry I did not see this earlier. If possible I'd like a cleaner solution, but this will do for now.