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/components/auth/default_current_user_provider_spec.rb

@@ -237,7 +237,7 @@ describe Auth::DefaultCurrentUserProvider do
     end
 
     after do
-      Discourse.redis.flushall
+      Discourse.redis.flushdb
     end
 
     it "should not update last seen for suspended users" do