Fork of Simple UDP proxy at http://aluigi.altervista.org/mytoolz.htm, with modifications required by Khan Academy

Downloaded from http://aluigi.altervista.org/mytoolz.htm (http://aluigi.altervista.org/mytoolz/sudppipe.zip)

cf. http://linux.softpedia.com/get/Internet/Proxy/Simple-UDP-proxy-pipe-11521.shtml

Khan Academy additions:

1. replace_plugin.c, based on example_plugins/rep_sudp.c.