bug#49536 - deadlock on rotate_and_purge when using expire_logs_days

Problem is that purge_logs implementation in ndb (ndbcluster_binlog_index_purge_file)
calls mysql_parse (with (thd->options & OPTION_BIN_LOG) === 0)) 
but MYSQL_BIN_LOG first takes LOCK_log and then checks thd->options

Solution in this patch, changes so that rotate_and_purge does not hold
LOCK_log when calling purge_logs_before_date. I think this is safe
as other "purge"-function(s) is called wo/ holding LOCK_log, e.g purge_master_logs

sql/log.cc

@@ -4481,6 +4481,9 @@ bool general_log_write(THD *thd, enum enum_server_command command,
 
 void MYSQL_BIN_LOG::rotate_and_purge(uint flags)
 {
+#ifdef HAVE_REPLICATION
+  bool check_purge= false;
+#endif
   if (!(flags & RP_LOCK_LOG_IS_ALREADY_LOCKED))
     pthread_mutex_lock(&LOCK_log);
   if ((flags & RP_FORCE_ROTATE) ||
@@ -4488,16 +4491,24 @@ void MYSQL_BIN_LOG::rotate_and_purge(uint flags)
   {
     new_file_without_locking();
 #ifdef HAVE_REPLICATION
-    if (expire_logs_days)
+    check_purge= true;
+#endif
+  }
+  if (!(flags & RP_LOCK_LOG_IS_ALREADY_LOCKED))
+    pthread_mutex_unlock(&LOCK_log);
+
+#ifdef HAVE_REPLICATION
+  /*
+    NOTE: Run purge_logs wo/ holding LOCK_log
+          as it otherwise will deadlock in ndbcluster_binlog_index_purge_file
+  */
+  if (check_purge && expire_logs_days)
   {
     time_t purge_time= my_time(0) - expire_logs_days*24*60*60;
     if (purge_time >= 0)
       purge_logs_before_date(purge_time);
   }
 #endif
-  }
-  if (!(flags & RP_LOCK_LOG_IS_ALREADY_LOCKED))
-    pthread_mutex_unlock(&LOCK_log);
 }
 
 uint MYSQL_BIN_LOG::next_file_id()