Add token to clear_call_for_reg( ).
Add token arg to set_call( ) and set_call_unsafe( ).
Add token arguments to more methods.
Remove long, soon-to-be out-dated comment.
Make used_inputs be in terms of computations.
Fix dot_graph_for_token.
Start using some token ids.
Make forward call edges use the computation.
Use pool<T>::reclaim_unmarked().