MFC r267667:
use .Mt to mark up email addresses consistently (part1)

PR: 191174
Submitted by: Franco Fichtner <franco at lastsummer.de>

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Moved mcgrab(1) into a separate directory -- our .mk infrastructure
doesn't currently have support for building multiple programs in a
single makefile.

While here, fixed manpages and makefiles (missing dependencies).

Fix a bug in the man page where we were not showing the correct flags
in the explanation. Several of the flags were -i, since it was a copy/paste
operation.

Update mctest and its associated script to have a base port to listen
on so that multiple copies can be run easily.

Update documentation with group and port arguments which are optional.

Updated the test to handle multiple sinks. The sinks cut their
transmissions by the number of them running so that they do not
overwhelm the source.

Added a simple shell script to kick off sinks on multiple hosts as
well as a source on the host where the shell script is run. The script
also collects the output of all the sinks and the source into files named
for the host on which the tests are run. A date is appended to each output
file to make it unique per run.

Add a manual page and a Makefile.

Add code to reflect packets back from the sink so that we can measure
round trip at the source.