Revert "Revert "Merge branch 'master' of https://github.com/discourse/discourse""

This reverts commit 20780a1eee.

* SECURITY: re-adds accidentally reverted commit:
  03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
  instead of the 03d26cd6 parent (which contains security fixes)

spec/models/topic_spec.rb

@@ -33,7 +33,7 @@ describe Topic do
 
       describe 'censored words' do
         after do
-          Discourse.redis.flushall
+          Discourse.redis.flushdb
         end
 
         describe 'when title contains censored words' do