attr filter "attrsfile" -> "file"

[A.L.M.Buxey at lboro.ac.uk]

Hi,

> >it should be there - that was a recent change.
> 
> I'm not seeing it... am I being dense?

no. as i said, it SHOULD be there. the README.rst isnt 100% locked to new features
as they arrive, sometimes there are delays ( the 'git what-changed' command is the
real oracle of changes to the HEAD ;-) ) 

alan