Detect if the platform stays the same only when site name changes.

Otherwise it is obvious that the target platform must be different if we run Migrate task.

platform/migrate.provision.inc

@@ -32,18 +32,20 @@ function drush_provision_drupal_pre_provision_migrate($platform, $new_name = NUL
   // If we are renaming the site, pick this up early.
   if (!is_null($new_name) && ($new_name != d()->name)) {
     drush_set_option('target_name', $new_name);
-  }
-  else {
-    // the site url stays the same
-    drush_set_option('target_name', d()->name);
+    drush_set_option('source_name', d()->uri);
 
-    // The platform stays the same
+    // Detect if the platform stays the same.
     if (d()->platform->name == $platform) {
       drush_log('Replacing the existing site on the same platform');
       // deploying over existing site.
       drush_set_option('deploy_replace_site', TRUE);
     }
   }
+  else {
+    // The site url stays the same, so the target platform
+    // must be different if we run Migrate task, right?
+    drush_set_option('target_name', d()->name);
+  }
 }
 
 /**