Changing how last-updated is tracked

[Sam Ruby]

Heads up.

I've changed the way venus tracks the last-update date of each weblog. 
Initially this means that if you have an existing venus installation, 
every weblog will look like it has not been updated in 90 days or 
whatever threshold you may have set (if you have set a threshold).

This will sort itself out as each weblog is updated.  You can force the 
issue by deleting the "sources" directory in your cache - this won't 
affect the entries in your cache, but will force every feed to be 
re-fetched on your next run.

  = = =

For those interested in the gory details, the issue is intermittent 
timeouts or HTTP level errors, followed by "not modified" responses.

"not modified" is clearly a success, but it is accompanied by no data. 
With "classic" planet, this was not an issue as the entire cache was 
read into memory, so determining when the weblog was last updated was 
easy.  Now I track the last updated date in the sources directory.

Caches created before this update won't have this information, so all 
feed will appear to never have been updated.

- Sam Ruby