FEATURE: allow users to specify a second hostname if needed

(very rarely needed feature, mostly for multisite and origin pull cdns)

app/models/global_setting.rb

@@ -23,7 +23,10 @@ class GlobalSetting
         hash[s] = val
       end
     end
-    hash["host_names"] = [ hostname ]
+    hostnames = [ hostname ]
+    hostnames << hostname2 if hostname2.present?
+
+    hash["host_names"] = hostnames
     hash["database"] = db_name
 
     hash["prepared_statements"] = !!self.db_prepared_statements

config/discourse_defaults.conf

@@ -46,6 +46,9 @@ db_prepared_statements = true
 # hostname running the forum
 hostname = "www.example.com"
 
+# backup hostname
+hostname2 =
+
 # address of smtp server used to send emails
 smtp_address =