Modify the dexter MPM to use an APR pipe for the pipe of death. This fixes

a bug I introduced earlier today, because it uses the APR_FILES_AS_SOCKETS
to let us use the pipe of death in a poll call.  With this change, dexter
becomes much more portable.  Dexter used to try to set the pipe
non-blocking on it's own, but it only tried one argument to fcntl.  There
are at least four different arguments to fcntl based on what platform you
are on.  APR gets rid of that ugliness for us.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85669 13f79535-47bb-0310-9956-ffa450edef68