mcjoin v2.1

Add validation of incoming multicast packets, verifying destination IP address of packet against expected multicast group for socket.

mcjoin v2.0

Massive refactor to add support for acting as both sender and receiver of multicast packets. This release makes mcjoin a standalone tool for verifying multicast connectivity.

Backwards compatible with v1.5 w.r.t. joining a single or multiple groups, with an optional -r, --restart=SEC. However, --long-opts have been removed and the -f FIRST and -n NUM options have been changed to command arguments on the form GROUP+NUM, which integrates better with the rest of the syntax.