_yp_dobind() checks to see if a fork() happens (by checking PIDs) and
invalidates all bindings if it finds itself in a newly created child
process. (This avoids sharing RPC client handles and socket descriptors
with the parent, which would be bad.) Unfortunately, it summarily
calls clnt_destroy() on the handles, which may result in the destruction
of a descriptor that isn't really a socket.
This is fixed by replacing the explicit call to clnt_destroy() with a
call to _yp_unbind(), which deals with potentially hosed socket descriptors
an a safe manner.
This is basically a one-liner. Once I confirm that it fixes Christoph's
problem, I'd like permission to put it in the 2.2-RELENG branch.
cc64a2bf11