Added check for 'sequence-item' in sort attribute.

silently ignoring them.

In particular, copy or moved object has new ID *before* it gets
added to the collection.

when seeking past the end of the "file".

Waaa.

length > 1.  Basically, the leading n-2 elements get added to the parents,
and the n-1th element is substituted for the object being traversed.
This is needed for making certain objects surrogates for others.
We use this to enter long-running transactions as we traverse objects.
It might be useful for creating "symbolic links".

Checked in a change (that I meant to check in before that fixes a bug
in the way '.' is handled.  Basically, '.' should be handled as
if it isn't really there.

handling to allow the protocol to be ommitted.