Supply proper limit on cursor initial query.

[ fix mongoid/mongoid#2849 ]
Collection#drop request should use the primary node
Update changelog
Capture command errors when sent to slave nodes

If we send a command, like drop, to a secondary node we get this
document as a response:

{"errmsg"=>"not master", "ok"=>0.0}

We should treat that operation error as a `ReplicaSetReconfigured`
error.
Update chaneglog
Merge branch '1.4.0-stable' of github.com:mongoid/moped into 1.4.0-stable