When assigning from one external to another, copy over internal values.
When get an external out of a container, return the external rather
than its internal value.
To resolve circular dependency from testing if is endpoint, created a
lightweight endpoint base class.
Got a case of deadlock if called an endpoint method on a reference to my own endpoint.
Corrected a couple of misspellings.
Constructor for external variables no longer needs a variable name.
Added copy method: sequence peered variables do not preserve
refernces and accesses to their reference types copy.