[krbdev.mit.edu #6369] lib/rpc should have way to register with secure rpcbind using unix domain socket

[Ezra Peisach via RT]

Under fedora 10 and other OS's - portmap has been replaced by rpcbind.

Security considerations have "improved" - requiring a loopback socket
and a reserved port (<1024) unless certain flags are given.

Looking at the sources for rpcbind - there is now support for a unix
domain socket connection - which is known to be local - and does not
therefore require a reserved port.

Either the rpc layer should be replaced with a newer implementation or 
the library could be shoehorned to attempt to use a unix domain socket
if present.