Get rid of __proto__ magic

[Loirooriol]

Reps is messing with __proto__ properties. See e.g. bug 1390027 and bug 1397772.

• Stop ignoring __proto__ enumerable own properties in object previews.
• Stop ignoring __proto__ own properties in object inspector.
• Stop adding misleading __proto__ own properties in object inspector. To reference the [[Prototype]] use a <prototype> property or something like that.

[nchevobbe]

See similar concerns in https://bugzilla.mozilla.org/show_bug.cgi?id=866334

[Loirooriol]

Fixed by #987 and #982. Also see #1000.