Since multiple processes can write logs simultaneously, and there
is no explicit synchronization between them, logs redirected to
stdout may interleave. When logging to the disk file, synchronization
is obtained by using a combination of O_APPEND and O_SYNC flags when
log file is being opened, which is not possible when <stdout>
redirection is in use.
So documentation is updated to cleanly notify that this is debug-only
feature, not for regular use
Alexander Pevzner
5d6123a046