Fix a few ReadPreference doc issues.

Author: behackett

doc/examples/high_availability.rst

@@ -180,7 +180,7 @@ Secondary Reads
 
 By default an instance of MongoReplicaSetClient will only send queries to
 the primary member of the replica set. To use secondaries for queries
-we have to change the :class:`~pymongo.read_preference.ReadPreference`::
+we have to change the :class:`~pymongo.read_preferences.ReadPreference`::
 
   >>> db = MongoReplicaSetClient("morton.local:27017", replicaSet='foo').test
   >>> from pymongo.read_preference import ReadPreference

pymongo/collection.py

@@ -1010,9 +1010,9 @@ def aggregate(self, pipeline):
         With :class:`~pymongo.replica_set_connection.ReplicaSetConnection`
         or :class:`~pymongo.master_slave_connection.MasterSlaveConnection`,
         if the `read_preference` attribute of this instance is not set to
-        :attr:`pymongo.ReadPreference.PRIMARY` or the (deprecated)
-        `slave_okay` attribute of this instance is set to `True` the
-        `aggregate command`_ will be sent to a secondary or slave.
+        :attr:`pymongo.read_preferences.ReadPreference.PRIMARY` or the
+        (deprecated) `slave_okay` attribute of this instance is set to `True`
+        the `aggregate command`_ will be sent to a secondary or slave.
 
         :Parameters:
           - `pipeline`: a single command or list of aggregation commands