check Remote.hasKeyCheap again

check Remote.hasKeyCheap again

In cd1676d604, it stopped using that to avoid surprising behavior
when the location log and remote content were out of sync.
But, it seems that may have changed some behavior users relied on as
well, and also Remote.hasKeyCheap should be faster than checking then
location log.

So, try Remote.hasKeyCheap first, and only if it does not have the key,
fall back to checking the location log. If the location log still thinks
it's present, go ahead and try to get it, so the user will see a failure
rather than silently skipping a file what whereis says is on the remote.

This does make slightly slower the case where the remote does not have
the key, and location log and Remote.hasKeyCheap agree, since it now
checks both. But only 1 stat slower.