Space trim and other unit tests. General space clean up.

The space unit tests now include checks on space invariants, in
particular relating to footprint and size.
Out-of-date comments have been removed.
This patch adds PrettySize and PrettyDuration methods to make these
strings more human readable.

Change-Id: I6bc05b2db0d0115b97d666b832fce57bcdd2e091