Create metaMap when creating class hierarchy instead of eachRelationship

[mtheoryx]

	/**
	 * Calls the callback for each relationship defined on the model.
	 *
	 * @method eachRelationship
	 * @for Model
	 * @param {Function} callback Function that takes `name` and `meta` parameters
	 * @param [binding] Object to use as `this`
	 * @static
	 */
	eachRelationship: function(callback, binding) {
		// Climb through class hierarchy looking for relationships
		// (###TODO: Might be nice to wire this up when creating the class hierarchy if possible.)
		var classProto = this.prototype;
		while (classProto && classProto.metaMap) {
			if (classProto.metaMap['_all']) {
				for (var j = 0, len = classProto.metaMap['_all'].length; j < len; ++j) {
					var name = classProto.metaMap['_all'][j];
					callback.call(binding, name, classProto.metaMap[name]);
				}
			}
			// Might be better to do this in initialization somewhere rather than on every eachRelationship call;
			// however, only costs one typeof and one string match each call
			if (typeof Object.getPrototypeOf !== 'function') {
				if (typeof 'test'.__proto__ === 'object') { // eslint-disable-line no-proto
					Object.getPrototypeOf = function(object) {
						return object.__proto__;  // eslint-disable-line no-proto
					};
				} else {
					Object.getPrototypeOf = function(object) {
						// May break if the constructor has been tampered with
						return object.constructor.prototype;
					};
				}
			}
			classProto = Object.getPrototypeOf(classProto);
		}
	},

Could be beneficial to avoid this on each, even though the performance hit is not too terrible