More additions to the NestedSet implementation: Added $node->makeRoot() which can be used when using many roots to detach a node from a tree and make it a root node itself.

Added support for transparently moving nodes between different trees when using many roots (EXPERIMENTAL!)

Ticket: 313

Doctrine_Node_NestedSet::getLastChild()

and Doctrine_Node_NestedSet::getPrevSibling()

Fixed a bug in Doctrine_Node_NestedSet::getRootValue() and setRootValue(). They were still using underscore property names (roo_column_name, ...).