Description:
------------
Multiple requests hitting the same FPM worker process will get logged (by php-fpm) with the last authenticated user seen instead of empty when there is no authenticated user for the current request.

Attached patch clears auth_user field (and also clears query_string), those two being the only char arrays not seeing initialization in fpm_request_accepting().

Test script:
---------------
# configure php-fpm to use only one worker and log access
restart php-fpm
curl -u user $php_fpm_page_via_nginx
curl $php_fpm_page_via_nginx
curl $php_fpm_page_via_nginx
# All logged access lines will show remote user to be "user"