Feature needs to report progress on an individual operation and allow the operation to be aborted.

A brief conversation with geert.bosch led to this:

WT_SESSION.progress(WT_SESSION session,
    void (*callback)(WT_SESSION *session, uint64_t count, bool *stop))

which declares a callback function long-running WiredTiger operations call with the session handle, a work-chunk count, and a boolean. If, on return, stop is true, the operation will be aborted, if that's possible.

I think the set of long-running operations are: compact, rebalance, salvage, upgrade and verify.

michael.cahill, alexander.gorrod, thoughts?