The previous version allowed for a response to be returned to the client, in case that R > 1 but only one worker has successfully returned a reply.
The previous version allowed for a response to be
returned to the client, in case that R > 1 but
only one worker has successfully returned a reply.

If we cannot get enough successful replies, but
receive `rexi_DOWN` or `rexi_EXIT` messages
instead, there will be a response with error code
500 (i.e.
`{"error":"unknown_error","reason":"rexi"}`)
from now on.

KlausTrainer/bigcouch,KlausTrainer/bigcouch,KlausTrainer/bigcouch,KlausTrainer/bigcouch,KlausTrainer/bigcouch,KlausTrainer/bigcouch