refactor(cursor): deduplicate properties shared by base cursors

There are a number of properties stored on the `CoreCursor` that
are duplicated in the private `s` member of the "native" cursor.
This changeset removes duplication.

Author: mbroadst

lib/command_cursor.js

@@ -216,11 +216,18 @@ CommandCursor.prototype.setReadPreference = function(readPreference) {
  * @return {CommandCursor}
  */
 CommandCursor.prototype.batchSize = function(value) {
-  if (this.s.state === CommandCursor.CLOSED || this.isDead())
+  if (this.s.state === CommandCursor.CLOSED || this.isDead()) {
     throw MongoError.create({ message: 'Cursor is closed', driver: true });
-  if (typeof value !== 'number')
+  }
+
+  if (typeof value !== 'number') {
     throw MongoError.create({ message: 'batchSize requires an integer', driver: true });
-  if (this.s.cmd.cursor) this.s.cmd.cursor.batchSize = value;
+  }
+
+  if (this.cmd.cursor) {
+    this.cmd.cursor.batchSize = value;
+  }
+
   this.setCursorBatchSize(value);
   return this;
 };
@@ -233,8 +240,9 @@ CommandCursor.prototype.batchSize = function(value) {
  */
 CommandCursor.prototype.maxTimeMS = function(value) {
   if (this.s.topology.lastIsMaster().minWireVersion > 2) {
-    this.s.cmd.maxTimeMS = value;
+    this.cmd.maxTimeMS = value;
   }
+
   return this;
 };