apache/spark — pull request #3194 by sarutak (2014-11-11 00:11:50+00:00)
Title: [SPARK-4329] Add indexing feature for HistoryPage

Current HistoryPage have links only to previous page or next page.
I suggest to add index to access history pages easily.

I implemented like following pics.

If there are many pages, current page +/- 4 page, head page and last page are indexed.

![2014-11-10 16 03 05](https://cloud.githubusercontent.com/assets/4736016/4986208/332b316c-6937-11e4-92e0-be2acc3718a2.png)
![2014-11-10 16 03 21](https://cloud.githubusercontent.com/assets/4736016/4986210/3951bb74-6937-11e4-8b4e-9f90d266d736.png)
![2014-11-10 16 03 39](https://cloud.githubusercontent.com/assets/4736016/4986211/3b196ad8-6937-11e4-9f81-74bc0a6dad5b.png)
![2014-11-10 16 03 49](https://cloud.githubusercontent.com/assets/4736016/4986213/40686138-6937-11e4-86c0-41100f0404f6.png)
![2014-11-10 16 04 04](https://cloud.githubusercontent.com/assets/4736016/4986215/4326c9b4-6937-11e4-87ac-0f30c86ec6e3.png)