Library unware of limit in datastore get

[wh5a]

Based on discussion at http://mattjibson.com/blog/2013/06/26/go-read-open-source-google-reader-clone/#comment-944610909, memcache access is limited to 1000 objects at once, and the memcache library needs to be made aware of this limit.

[maddyblue]

I've changed the title of this issue to be the actual error, which has been fixed. Datastore gets were limited to 1000 at a time. I believe goon now supports this.