HAMMER Util - Add new features, fix history retention bug in prune
* The prune code was not retaining the fine-grained history between
the last snapshot and current.
* Add a new PFS config variable called 'prune-min' which may be used
to set the minimum fine-grained history retention, in seconds. The
hammer prune code will not prune inbetween any snapshots that are
within the fine-grained retention period.
* The mirror-stream directive now automatically loops and reconnects
if the network connection fails.
* The mirror-stream directive now attempts to break-up a large initial
bulk transfer into smaller transfers, inserting synchronization points
so a failure in the middle of the large bulk transfer does not require
starting from scratch again.
* The show directive (show btree) now takes an optional localization[:objid]
argument (specified in hex). If specified the directive will search
the B-Tree for the key, printing nodes as it goes, and then continue
with a normal iteration.