Nginx does not re-open log files on SIGUSR1.

[Piotr Karbowski]

Hi there.

I think this is bug, I saw that after logrotate (which on the end 
running SIGUSR1 on master process) my access log is empty. However if I 
do SIGHUP it starts working. Looks like Nginx does not re-open logfiles 
after USR1.

I was able reproduce it multiple times, nginx version 0.8.53, I am not 
sure if it was working in older versions.

-- Piotr.