tree->layout

tree ->layout:

Recompute the layout of the tree. This method is normally called from tree->compute and sends the following three messages to tree<-display_root:

node->compute_level Update the node<-level slots

node->compute_size Compute the sizes of all nodes

node->compute_layout Place the nodes

node`->`compute_level	Update the node`<-`level slots
node`->`compute_size	Compute the sizes of all nodes
node`->`compute_layout	Place the nodes