Fix build with nginx-0.8.0 and versions older than nginx-0.7.60.
Fix build with nginx-0.8.0 and versions older than nginx-0.7.60.

Found by build farm for nginx modules.

ainoya/ngx_cache_purge,FRiCKLE/ngx_cache_purge,ainoya/ngx_cache_purge,FRiCKLE/ngx_cache_purge,lilien1010/ngx_cache_purge,lilien1010/ngx_cache_purge