Acceptor names

[Greg Hudson]

The project proposal for acceptor name changes is ready for review at:

http://k5wiki.kerberos.org/wiki/Projects/Acceptor_Names

There were several possible places to implement
ignore_acceptor_hostname; after discussion and consideration, I settled
on krb5_rd_req.  rd_req will assume that the second principal of a
KRB5_NT_SRV_HST principal is a hostname and can be ignored for keytab
matching purposes if ignore_acceptor_hostname is set.