Tree.Sortable: Add deep sorting.

Tree.Sortable#sort() sorts every node in the tree.

Tree.Sortable#sortNode() now has a `deep` option. If set to `true`,
every node in the specified node's hierarchy will be sorted instead of
just the children of the specified node.
Merge branch 'dev-3.x' of github.com:yui/yui3 into tree-deep-sort

Conflicts:
	src/tree/HISTORY.md
Tree.Sortable: Preserve `this` object for comparators.
Typo.
Merge branch 'tree-deep-sort' of git://github.com/rgrove/yui3 into dev-3.x
Merge branch 'tree-sortable-comparator' of git://github.com/rgrove/yui3 into dev-3.x

Conflicts:
	src/tree/HISTORY.md
	src/tree/js/extensions/tree-sortable.js
Build tree-sortable.