How swift objects are layed out on filesystem

Implementation details on how Swift puts files on the filesystem.

Based on an email from John Dickisnon on the openstack mailing list.

(Also trims a lot of trailing whitespace from several lines in
this file).

Cherry-picked from https://review.openstack.org/19046

Change-Id: I835d00cfc381e40501baa2a05944a8e0be018844