store_flatfile needs v3 fixes ported up

[baallan]

The flatfile store needs to be updated with changes from v3. It also needs to have rollover support added. It also needs to not require component_id if producername is present instead.

after these fixes, store_flatfile can then be used to selectively and losslessly roll data into splunk via its universal forwarder without requiring pipes or 100% splunk uptime.