use more consistent override

Author: yyx990803

src/index.js

@@ -1,5 +1,5 @@
 import util, { warn, mapParams } from './util'
-import initMixin from './mixin'
+import applyOverride from './override'
 import Recognizer from 'route-recognizer'
 import Route from './route'
 import Transition from './transition'
@@ -563,7 +563,7 @@ Router.install = function (externalVue) {
     return
   }
   Vue = externalVue
-  initMixin(Vue)
+  applyOverride(Vue)
   View(Vue)
   Link(Vue)
   util.Vue = Vue

src/mixin.js

@@ -0,0 +1,34 @@
+export default function (Vue) {
+
+  const _ = Vue.util
+
+  const init = Vue.prototype._init
+  Vue.prototype._init = function (options) {
+    const root = options._parent || options.parent || this
+    const route = root.$route
+    if (route) {
+      route.router._children.push(this)
+      if (!this.$route) {
+        if (this._defineMeta) {
+          // 0.12
+          this._defineMeta('$route', route)
+        } else {
+          // 1.0
+          _.defineReactive(this, '$route', route)
+        }
+      }
+    }
+    init.call(this, options)
+  }
+
+  const destroy = Vue.prototype._destroy
+  Vue.prototype._destroy = function () {
+    if (!this._isBeingDestroyed) {
+      const route = this.$root.$route
+      if (route) {
+        route.router._children.$remove(this)
+      }
+      destroy.apply(this, arguments)
+    }
+  }
+}