Log Message:
Import mbuffer-20140310 into pkgsrc, packaged by Brian Bennett.

mbuffer is a tool for buffering data streams with a large set of
unique features:

 * direct support for TCP based network targets (IPv4 and IPv6)
 * ability to send to multiple targets in parallel (distribution mode)
 * support for multiple volumes
 * I/O rate limitation
 * high/low watermark based restart criteria
 * configurable buffer size
 * on the fly MD5 hash calculation
 * highly efficient, multi-threaded implementation

It is especially useful, if you are writing backups to fast tape drives
or libraries.