Add a virtual 'length' property to Duktape/C functions if they don't have a concrete property of that name.  Ideally the number could be overwritten with a concrete property value, but currently the value is non-writable.  Making it writable is trivial, but putprop needs to be fixed so that overwriting a virtual property works.  Currently putprop assumes that if an own property is writable, it cannot be a virtual property.
a simple testcase to check that built-in function prototype is Function.prototype (this prevents using an intermediate prototype before Function.prototype to provide custom properties for Duktape/C functions)
update description of Duktape/C function properties
release note update