Note scope of temporary variables.
Currently only the following distinctions are made:
0 outer level: args and user-declared temps
1 block args and doLimiT temps
-1 a block temp that is no longer active
-2 a block temp that held limit of to:do:
For messageNodes masquerading as variables for the debugger.
For now we let this through - ie we allow stores ev
into args. Should check against numArgs, though.