Under certain conditions (possibly associated with heavy load), ypserv will
fork() child processes that don't exit like they're supposed to. I think
this is because of some suspect logic in the ypproc_all procedure. I updated
it to use what I hope is a more bulletproof approach.
Also tweaked yp_svc_run() a little so that the 'are we a child?' test happens
at every pass through the for(;;) loop, not just immediately after returning
from svc_getreqset2().
fdde373153