aliases: fix blacklists when aliasing tags.

When aliasing a tag, update any blacklists containing the old tag to use
the new tag.

app/logical/tag_mover.rb

@@ -13,6 +13,7 @@ class TagMover
       move_artist!
       move_wiki!
       move_saved_searches!
+      move_blacklists!
       move_posts!
     end
   end
@@ -58,6 +59,10 @@ class TagMover
     SavedSearch.rewrite_queries!(old_tag.name, new_tag.name)
   end
 
+  def move_blacklists!
+    User.rewrite_blacklists!(old_tag.name, new_tag.name)
+  end
+
   def merge_artists!
     old_artist.lock!
     new_artist.lock!