too many command objects

Currently each user gets a complete set of command objects at the start of a session. Ouch! This could make things rather slow as the capabilities of the Ark grow.

The good news is that commands don't do much. They don't need session state at all--that's kept in the portal, Env and the stack of Evaluators. So lets simply require that, like servlets, commands are thread safe. (Which I believe all existing commands already are.) A small change to the initialization process of Env and things are much better.

Now, what about commands specific to a type of rolon? We could have a static variable on a rolon (a HashMap, why not) which holds commands specific to that type of rolon. Another small change to Env and we've just made the Ark that much more extensible. And we've added another dimension to the applicability of commands.

Bill