Show in tab that a file was not saved yet

If a file is not saved yet, an asterisk is shown before the file name.

This solves #2938 

![screenshot from 2014-09-26 20 11 57 v01](https://cloud.githubusercontent.com/assets/8182792/4429594/4983bf3a-45f4-11e4-9049-649a11b1b910.png)


review @ussuri @devoncarew 

Can you change this to just `font-style: italic`? I'll do some tweaking after it lands.