message: Populated old context from current
  Now it's only set when gesturing/pressing back the old stuff comes from the current.
diff: @@ -46,7 +46,7 @@ class Scene extends React.Component<NavigationMotionProps, NavigationMotionState
  }
  willNavigate({crumb: targetCrumb}) {
  var {crumb, navigationEvent} = this.props;
  - var {crumbs} = navigationEvent.stateNavigator.stateContext;
  + var {crumbs, nextCrumb} = navigationEvent.stateNavigator.stateContext;
  if (targetCrumb === crumb && crumb < crumbs.length) {
  var changed = !this.state.navigationEvent;
  if (!changed) {
  @@ -60,7 +60,7 @@ class Scene extends React.Component<NavigationMotionProps, NavigationMotionState
  if (changed) {
  var {stateNavigator} = navigationEvent;
  var tempNavigator = new StateNavigator(stateNavigator, stateNavigator.historyManager);
  - tempNavigator.stateContext = Scene.createStateContext(crumbs, crumb);
  + tempNavigator.stateContext = Scene.createStateContext(crumbs, nextCrumb, crumb);
  tempNavigator.configure = stateNavigator.configure;
  tempNavigator.onBeforeNavigate = stateNavigator.onBeforeNavigate;
  tempNavigator.offBeforeNavigate = stateNavigator.offBeforeNavigate;
  @@ -72,7 +72,7 @@ class Scene extends React.Component<NavigationMotionProps, NavigationMotionState
  }
  }
  }
  - static createStateContext(crumbs: Crumb[], crumb: number) {
  + static createStateContext(crumbs: Crumb[], nextCrumb: Crumb, crumb: number) {
  var stateContext = new StateContext();
  var {state, data, url, title} = crumbs[crumb];
  stateContext.state = state;
  @@ -81,11 +81,15 @@ class Scene extends React.Component<NavigationMotionProps, NavigationMotionState
  stateContext.title = title;
  stateContext.crumbs = crumbs.slice(0, crumb);
  stateContext.nextCrumb = crumbs[crumb];
  + var {state, data, url} = nextCrumb;
  + stateContext.oldState = state;
  + stateContext.oldData = data;
  + stateContext.oldUrl = url;
  if (crumb > 1) {
  var {state, data, url} = crumbs[crumb - 1];
  - stateContext.previousState = stateContext.oldState = state;
  - stateContext.previousData = stateContext.oldData = data;
  - stateContext.previousUrl = stateContext.oldUrl = url;
  + stateContext.previousState = state;
  + stateContext.previousData = data;
  + stateContext.previousUrl = url;
  }
  return stateContext;
  }
  