Fix for BUG#2145 "mysqld becomes unreliable if unable to create a relay log when replic starts":

release the mutex before exiting the function, or it will be kept forever
(=> START SLAVE, STOP SLAVE, etc will hang).


sql/slave.cc:
  release the mutex before exiting the function, or it will be kept forever
  (=> START SLAVE, STOP SLAVE, etc will hang).

sql/slave.cc

@@ -1321,6 +1321,7 @@ int init_relay_log_info(RELAY_LOG_INFO* rli, const char* info_fname)
 	       1 /* no auto events */,
                max_relay_log_size ? max_relay_log_size : max_binlog_size))
   {
+    pthread_mutex_unlock(&rli->data_lock);
     sql_print_error("Failed in open_log() called from init_relay_log_info()");
     DBUG_RETURN(1);
   }