Modules: added a session object for js_periodic handler.

Modules: added a session object for js_periodic handler.

Now js_periodic handler is provided with a session object as its first
argument. Session object can be used to access variables created with
js_set, js_var or map directives.

example.conf:
    js_var $js_var  JS-VAR;

    location @periodics {
        js_periodic main.handler interval=60s;
    }

example.js:
    function handler(s) {
        ngx.log(ngx.INFO, s.variables.js_var);
    }