tracelib: support systems < 10.6 by using djb's self-pipe trick instead of EVFILT_USER
tracelib: support systems < 10.6 by using djb's self-pipe trick instead of EVFILT_USER

See http://cr.yp.to/docs/selfpipe.html

git-svn-id: 620571fa9b4bd0cbce9a0cf901e91ef896adbf27@108029 d073be05-634f-4543-b044-5fe20cf6d1d6

neverpanic/macports-base,neverpanic/macports-base,danchr/macports-base,danchr/macports-base,macports/macports-base,macports/macports-base