To allow classes to have methods that match built-in names, yet, still
disallow them outside of defclass, keep an internal state whether
builtins are allowed in the current context.
By default, this is false. But defclass will set it to True when it
compiles its body, and set it back to the previous value when it's done
with that. We need to set back to the previous value to allow nested
defclasses to work properly.
This closes#783.
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
b92049d119