DEV: haring: add a new option "-r" to automatically repair broken files

DEV: haring: add a new option "-r" to automatically repair broken files

In case a file-backed ring was not properly synced before being dumped,
the output can look bogus due to the head pointer not being perfectly
up to date. In this case, passing "-r" will make haring automatically
skip entries not starting with a zero, and resynchronize with the rest
of the messages.

This should be backported to 2.6.