merge r2972, r2994, r3133, r3142, r3143, r3174, r3175, r3176: various perl fixes: *) fix ngx_http_send_special() for subrequests handled by perl *) allow perl "sub{..." *) restore environ, this fixes segfault on reconfiguration failure when perl module creates new environment *) optimize error handling *) use ngx_conf_set_str_array_slot() for perl_require *) allow several perl_modules