[Federated-fs] FSN and filesets

[Ellard, Daniel]

The current document defines fileset first, and then FSN, and then says
that these two terms are used interchangably.  I'd like to scrub the
document and fix the usage to keep these terms distinguished.  A fileset
is the unit of management and abstraction for data, and a FSN is a name
for a fileset.  It's useful to be able to distinguish between the thing
and the name of the thing.

Thoughts?
	-Dan