add Colm's explanation of the cache_info structure from his explaination on dev@

/* cache info information */

typedef struct cache_info cache_info;

struct cache_info {

    /** 

     * HTTP status code of the cached entity. Though not neccessarily the

     * status code finally issued to the request. 

     */

    int status; 

    /** 

     * the original time corresponding to the 'Date:' header of the request 

     * served 

     */

    apr_time_t date; 

    /** a time when the cached entity is due to expire */

    apr_time_t expire;

    /** r->request_time from the same request */

    apr_time_t request_time;

    /** apr_time_now() at the time the entity was acutally cached */

    apr_time_t response_time;

};