Implement performance enhancement for commands

[marinier]

As discussed here and implemented in commit 08ae031, command performance can be significantly improved. This is unlikely to matter for commands that aren't being called at runtime, but for those that are (like the log command that was fixed), this can make a huge difference. And if we do them all this way, we would be able to eliminate the instanceof call in Utils.parseAndRun().

The next most critical command is probably print, which I know SID uses on the RHS.