Store hash of URL in the boost_cache_relationships table

Store the time stamp too; will allow for smarter operations if the view shrinks in size. If the time stamp for that entry doesn't match the rest, then its old and needs to be cleared. Something like 5x older then the expiration. Older then 3 days would be the minimum. Trim on cron; update on cache creation.

Better yet, instead of flushing it, check the actual view first; only if the view no longer contains the node will that entry be removed.

Best idea today... remove the entires from the relationship table when that view is flushed. Still need the other parts of this though, just makes the odds of something falling through the cracks even less.

Covers all cases expect for when a view shrinks in size (using pager; url no longer valid)... will have to cover that somehow; most likely a timestamp db scan on cron. Open to idea on this one. Alt would be a hook for views inside boost_cache_kill(), but thats not 100% accurate then.

committed