Merge from vendor branch TNF:

Merge from vendor branch TNF:
Import bmon from pkgsrc-wip.  Packaged by hsaliak at gmail dot com, and
slightly modified by me.

Bmon is an interface bandwidth monitor.  It is able to generate and
draw three types of diagrams: The overview diagram which is a list of
all interfaces and their send/receive rates.  A very MRTG like
graphical diagram in ASCII showing the rate over a specific time
period in a bar diagram.  The details diagram which contains all
counters of an interface such as total bytes sent/received, errors,
compressed packets and so on.