- Bformat: must stringize arguments after format string
 - defun: Builtin again so we have a name tag at the function object
 - while: Builtin again due to mysterious non-working of lisp-defined while
 - divide: do return reciprocal value with single argument
 - changed error() calls and first args to new syntax (format, args)
 - made regtests/002 pass (took out factor call, which this one doesn't have)