attr filter "attrsfile" -> "file"

[Alan DeKok]

Arran Cudbard-Bell wrote:
>> Can we at least maintain backwards compatibility for one major version to read the old filenames? Surely it can't be that hard to have a short lookup table from the old names?
> 
> So then you take over maintence of a v3.x system and all the configurations are in this weird format and you can't really see how it works and, and...

  The config system has provisions for backwards compatibility.  We can
leverage that, but deprecate the old system.

  That being said, there is config in 3.x that is backwards compatible
with config from 0.x.  That's wrong, and will be fixed.

  For other things, like "User-Password", it *causes* problems.  People
read decade-old "howto's", and create broken configurations.  It's a
good idea to get that fixed.

  Alan DeKok.