Check-in [e6ade010a0]

A supporting introspector is also added, **info object creationid**, which
returns the creation ID of any existing object. It also applies to classes.
Again, note that creation IDs are _always_ system-allocated and are _never_
guaranteed to be unique between interpreters, either in multiple processes or
in the same thread or process; they are only ever locally unique.

# Example

    oo::class create LabelEqual {
		constructor {label} {
			set [my varname label] $label
		}
        private {
		    variable label
			method getLabel {} {
			    return $label
			}
		}
		method equals {other} {
			expr {$label eq [$other getLabel]}
		}
	}

	oo::class create Evaluated {
		superclass LabelEqual
		# Poorly chosen variable name! Happens too easily in real life
		variable label
		constructor {expression} {
			next $expression
			set label [expr $expression]
		}
	    method value {} {
			return $label
		}
	}

	set expr1 [Evaluated new {1 + 2 + 3}]
	set expr2 [Evaluated new {3 + 2 + 1}]
	puts "one is two? [$expr1 equals $expr2]"
	# Prints: one is two? 0
	puts "one=[$expr1 value] two=[$expr2 value]"
	# Prints: one=6 two=6
	puts [info vars [info object namespace $expr1]::*]
	# Prints something like: {::oo::Obj13::11 : label} ::oo::Obj13::label
	catch {$expr2 getLabel} msg
	puts $msg
	# Prints: unknown method "getLabel": must be destroy, equals or value

# Implementation

See the [`tip-500` branch](https://core.tcl.tk/tcl/timeline?r=tip-500).

# Copyright

This document has been placed in the public domain.