Issue #1331370 by beejeebus, plach: Fixed [Upgrade path broken] Stored include...

Issue #1331370 by beejeebus, plach: Fixed [Upgrade path broken] Stored include paths need to be updated to /core before running the upgrade path.

core/includes/update.inc

@@ -101,6 +101,12 @@ function update_prepare_d8_bootstrap() {
       ),
     );
     if ($has_required_schema) {
+      // Bootstrap variables so we can update theme while preparing the update
+      // process.
+      drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
+      // Update the dynamic include paths that might be used before running the
+      // proper update functions.
+      update_prepare_stored_includes();
       // Update the environment for the language bootstrap if needed.
       update_prepare_d8_language();
 
@@ -127,6 +133,22 @@ function update_prepare_d8_bootstrap() {
   }
 }
 
+/**
+ * Fix stored include paths to match the "/core" migration.
+ */
+function update_prepare_stored_includes() {
+  // Update language negotiation settings.
+  foreach (language_types() as $language_type) {
+    $negotiation = variable_get("language_negotiation_$language_type", array());
+    foreach ($negotiation as $id => &$provider) {
+      if (isset($negotiation[$id]['file']) && $negotiation[$id]['file'] == 'includes/locale.inc') {
+        $negotiation[$id]['file'] = 'core/includes/locale.inc';
+      }
+    }
+    variable_set("language_negotiation_$language_type", $negotiation);
+  }
+}
+
 /**
  * Prepare Drupal 8 language changes for the bootstrap if needed.
  */