Change hot_standby default value to 'on'

This goes together with the changes made to enable replication on the
sending side by default (wal_level, max_wal_senders etc) by making the
receiving stadby node also enable it by default.

Huong Dangminh

src/backend/utils/misc/guc.c

@@ -1571,7 +1571,7 @@ static struct config_bool ConfigureNamesBool[] =
 			NULL
 		},
 		&EnableHotStandby,
-		false,
+		true,
 		NULL, NULL, NULL
 	},
 

src/backend/utils/misc/postgresql.conf.sample

@@ -254,7 +254,7 @@
 
 # These settings are ignored on a master server.
 
-#hot_standby = off			# "on" allows queries during recovery
+#hot_standby = on			# "off" disallows queries during recovery
 					# (change requires restart)
 #max_standby_archive_delay = 30s	# max delay before canceling queries
 					# when reading WAL from archive;