This fixes #986(show year in notebook tree dates)

Linking this commit with PR #1076  to retain the comments.

@gordonwoodhull, Closed old PR#1076 as that branch was messed up and raising this new PR for the fresh commit in which the subtle bug you pointed out has been fixed. Now you can see the year in the date for older versions from a different year, only and whenever date is shown. Below is a screenshot generated from dummy data : 

![untitled](https://cloud.githubusercontent.com/assets/1859165/5050123/87dde962-6c51-11e4-8559-a409f3eeaf18.png)