*) Feature: now the "directio" directive works on Linux.
*) Feature: the $pid variable.
*) Bugfix: the "directio" optimization that had appeared in 0.7.15 did not work with open_file_cache.
*) Bugfix: the "access_log" with variables did not work on Linux; the bug had appeared in 0.7.7.
*) Bugfix: the ngx_http_charset_module did not understand quoted charset name received from backend.