Report more detail about disk errors, especially the disker ID and db path.

Report more detail about disk errors, especially the disker ID and db path.

On partial writes, try to write the leftovers a few times before giving up.
The caller is unlikely to employ a different strategy, and we can do that
faster. Current callers simply give up and declare an error. Partial disk
writes seem to be typical on overflowing disks, but there may be other
conditions we have not observed in the lab yet.