The checks to see if files were out of date in the attibute cache
was wrong because the cache-breaker data wasn't getting stored
correctly. Additionally, when the cache-breaker triggered, the
old file data was being leaked.
This is a big refactoring of the attribute file cache to be a bit
simpler which in turn makes it easier to enforce a lock around any
updates to the cache so that it can be used in a threaded env.
Tons of changes to the attributes and ignores code.
