cache bugcache suggestions across 

I noticed a lot (as in hundreds... possibly thousands) of redundant search terms being passed to `refdata.get_suggested_bugs()` in the `log_references` loop in `log_parser.tasks`. There are also likely redundant searches occurring across logs but that will require a persistent RAM cache (memcached or whatever...) to resolve, this probably also needs to be done. For now, this branch implements a search cache across all the logs parsed by a single instance of `tasks.parse_log`. 

I removed the timestamp from the search terms but kept it in the `open_bugs_suggestions` and `closed_bugs_suggestions` keys, this might actually be required, cannot remember, if it's needed we can just remove the replace statement. There are still redundant search queries occurring with the same timestamps so there will be a performance improvement from these changes.