other way of indicating unique part in filename

[GoogleCodeExporter]

'unique' part in the filename was indicated by asteriks ('*') in bots<-3.2.
Now: use {unique}. 
Reason for change: 
- more options in formatting via python formatstrings
- more inline with other options
old way (asteriks) will keep working 

Original issue reported on code.google.com by hjebb...@gmail.com on 28 Mar 2015 at 2:54