More code and comment cleanups.  Notable changes:

FileCache:  removed the currentsize attribute.  It was initialized
to 0 but never updated.  Some tests referenced it, but since it was
always 0 those tests weren't getting any good from it.  Don't
recall (or never knew) what its intended purpose may have been.

FileCache.remove():  Repaired major bug.  This mistakenly stored
the "this disk block is free now" status byte into the start of
the serialized Object record's end_tid field (incorrect seek
offset).  The in-memory structures were correct then, but got out
of synch with the disk file; the latter then still claimed to have
info for a "live" object revision, but that revision was actually
dead, and the info on disk had a corrupt end_tid value.