Stats counters are properties of vault operation such as a snapshot, not the vault itself. Remove them from the vault structure and put them into a <code>job</code> structure which is obtained through a parameter, with a default value pointing to an "anonymous job" for convenience.

<code>tag-snapshot!</code> must then be passed a job object in order to gather stats from it; if <code>#f</code> is supplied, then no stats are recorded in the snapshot metadata.

Make <code>archive-log!</code> call a callback in the job object in scope for every log message, too. The interactive frontend can provide a handler that displays them to the user.

<hr /><i>alaric added on 2012-06-06 19:43:45 UTC:</i><br />
Done in [e99bd62896] and [17023073431f].

In addition, I moved the "configuration" flags from the vault object (check-correctness?, store-atime? and store-ctime?) into the job object.