Link to create blob from blob show

After:

![screenshot from 2014-11-02 19 15 43 after](https://cloud.githubusercontent.com/assets/1429315/4876245/72bc8118-62bc-11e4-82fb-a02cef6b641d.png)

Before:

![screenshot from 2014-11-02 19 15 36 before](https://cloud.githubusercontent.com/assets/1429315/4876246/77f1fbf4-62bc-11e4-9310-8b7dd2e89083.png)

This would make it analogous to many other show pages which also have a create new button, like tree show:

![screenshot from 2014-11-02 19 15 52 tree](https://cloud.githubusercontent.com/assets/1429315/4876251/8713dcd8-62bc-11e4-9531-c72ba06e3756.png)

and wiki pages:

![screenshot from 2014-11-02 19 16 14 wiki](https://cloud.githubusercontent.com/assets/1429315/4876252/8bd7b5aa-62bc-11e4-8039-fe0e4e8d9708.png)