TraitListObject._validate_length has bad error message

[mdickinson]

The _validate_length method of TraitListObject uses object in its error message, but in that context, object is not a local variable but instead refers to the built-in object type.

This results in error messages that look like:

The 'windows' trait of a type instance must be a list of items which are an envisage.ui.tasks.task_window.TaskWindow or None, but you attempted to change its length to -1 elements.

Code link:

traits/traits/trait_list_object.py

Lines 892 to 893 in 94a3dca

	class_of(object),
	self.trait.full_info(object, self.name, Undefined),