New failure detection algorithm for ng_one2many.

[Evgeny Dolgopiat]

I wrote new failure detection algorithm based on heartbeat signal for
ng_one2many node. Features:

- automatic detection of failures;
- automatic detection of recoveries;
- detection of point of failure (see diagnostics in man page);
- configurable timing parameters of failure and recovery detection;
- you can create your own heartbeat packet or use default;
- you can set your rules for detecting that incoming packet is hearbeat  
packet;
- heartbeat algorithm can be used for different network layers (not only 
ethernet layer).

Patches for src and man page at 
http://www.watson.org/~ilmar/download/ng_one2many.tgz
These patches for CURRENT, but you can compile patched files in 5.3.