Use FileRepository where we assume other file semantics

Use FileRepository where we assume other file semantics

When the surrounding code is already heavily based upon the
assumption that we have a FileRepository (e.g. because it
created that type of repository) keep the type around and
use it directly.  This permits us to continue to do things
like save the configuration file.

Change-Id: Ib783f0f6a11acd6aa305c16d61ccc368b46beecc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>