Set prototype internal property when creating objects.
Create function objects with initial properties.

Set "length" and "prototype" and "prototype.constructor" properties.

Only for functions, not script functions or C-functions.
Define some global functions and values.
Improve stackidx function to return "undefined" for out-of-bounds accesses.
Add constructors called with 'new' keyword.

Support built-in constructors that create their own objects. They get
called without a this object, which they should create and push on the
stack.