I added test cases for the bug, of course, and I also needed to change
the definition and tests for RBTreeNodeChain::RBT_MAX_LEVEL because this
fix changed the tree structure when the root node is contained.

The special case in find() and insert() due to the root name is
counter intuitive, but for now we need it to make it work correctly.
In near future for performance enhancements, I have a plan to update
the internal to support the notion of "label sequences" where a
sequence may not always be terminated with ".".  I expect we can
simply the code around this when this happens.

Proposed changelog:
{{{
  195.?	[bug]		jinmei
	b10-auth, src/lib/datasrc: the backend of the in-memory data
	source could not handle the root name.  As a result b10-auth could
	not work as a root server when using the in-memory data source.
	(Trac #683, git TBD)
}}}