PYTHON-2734 Document that find_raw_batches now sends user-specified R… (#634)

(cherry picked from commit b69d00d)

Author: prashantmital

pymongo/collection.py

@@ -1546,6 +1546,10 @@ def find_raw_batches(self, *args, **kwargs):
         .. note:: find_raw_batches does not support sessions or auto
            encryption.
 
+        .. versionchanged:: 3.12
+           Instead of ignoring the user-specified read concern, this method
+           now sends it to the server when connected to MongoDB 3.6+.
+
         .. versionadded:: 3.6
         """
         # OP_MSG with document stream returns is required to support

test/test_cursor.py

@@ -1526,6 +1526,7 @@ def test_collation_error(self):
             next(self.db.test.find_raw_batches(collation=Collation('en_US')))
 
     @client_context.require_version_min(3, 2)
+    @client_context.require_no_mmap   # MMAPv1 does not support read concern
     def test_read_concern(self):
         self.db.get_collection(
             "test", write_concern=WriteConcern(w="majority")).insert_one({})