HAMMER Util - Bulk transfer, SIGPIPE, more features.

HAMMER Util - Bulk transfer, SIGPIPE, more features.

* Add -B option for initial bulk transfer in a mirror-stream

* The parent process in a mirror-stream and mirror-copy operation
  now ignores SIGPIPE

* Use the smaller of ctime or mtime when calculating the real timestamp
  for a snapshot softlink in a prune operation.

* Sleep an additional 15 seconds before reconnecting a failed connection
  in a mirror-stream operation.