Change internal cache struct to fix restoring mixed containers

When different pjax containers were used for pjax navigations, the
popstate restoring mechanism would get confused as to in which container
to restore some particular HTML. I tried to remedy this by reading the
target container from `previousState` on "back" navigations, however
this was subject to at least a couple of flaws:

1. It would break if `previousState` was done via replaceState, which
   replaces content in a container but doesn't add a history entry.

2. It doesn't handle the case where user jumps several steps of history
   stack (e.g. by holding the "Back" button pressed and choosing from the
   drop down menu).

A more solid solution to knowing where to restore particular cached HTML
is to save the information about the container that the HTML was saved
from in the first place. This adds the container selector information to
the cache, forming a pair with cached contents for each history entry.

Author: mislav

jquery.pjax.js

@@ -424,29 +424,27 @@ function onPjaxPopstate(event) {
 
   var previousState = pjax.state
   var state = event.state
+  var direction
 
   if (state && state.container) {
     // When coming forward from a separate history session, will get an
     // initial pop with a state we are already at. Skip reloading the current
     // page.
     if (initialPop && initialURL == state.url) return
 
-    var direction, containerSelector = state.container
-
     if (previousState) {
       // If popping back to the same state, just skip.
       // Could be clicking back from hashchange rather than a pushState.
       if (previousState.id === state.id) return
 
       // Since state IDs always increase, we can deduce the navigation direction
       direction = previousState.id < state.id ? 'forward' : 'back'
-      if (direction == 'back') containerSelector = previousState.container
     }
 
-    var container = $(containerSelector)
-    if (container.length) {
-      var contents = cacheMapping[state.id]
+    var cache = cacheMapping[state.id] || []
+    var container = $(cache[0] || state.container), contents = cache[1]
 
+    if (container.length) {
       if (previousState) {
         // Cache current container before replacement and inform the
         // cache which direction the history shifted.
@@ -564,7 +562,7 @@ function cloneContents(container) {
   cloned.find('script').each(function(){
     if (!this.src) jQuery._data(this, 'globalEval', false)
   })
-  return cloned.contents()
+  return [container.selector, cloned.contents()]
 }
 
 // Internal: Strips named query param from url

test/unit/pjax.js

@@ -253,7 +253,7 @@ if ($.support.pjax) {
     }, 0)
   })
 
-  asyncTest("mixed containers", 4, function() {
+  asyncTest("mixed containers", 6, function() {
     navigate(this.frame)
     .pjax({ url: "fragment.html", container: "#main" })
     .pjax({ url: "aliens.html", container: "#foo" }, function(frame) {
@@ -262,6 +262,11 @@ if ($.support.pjax) {
     .back(-1, function(frame) {
       equal(frame.$("#main > #foo").text().trim(), "Foo")
     })
+    .pjax({ url: "env.html", replace: true, fragment: "#env", container: "#bar" }, function(frame) {
+      // This replaceState shouldn't affect restoring other popstates
+      equal(frame.$("#main > #foo").text().trim(), "Foo")
+      ok(JSON.parse(frame.$("#bar").text()))
+    })
     .back(-1, function(frame) {
       equal(frame.$("#main > ul > li").first().text(), "home")
     })