Add a kadm5 RPC for purging old keys from the KDB (e.g., from
change_password -keepold), and add a kadmin CLI command for it.

Keeping ticket open because an automated test needs to be added.

Long-term future work includes start/expire dates on keys, or
not-yet-valid flags.

https://github.com/krb5/krb5/commit/1cc59c12550c828d487c622990d83481e8bbb6c5
Commit By: tlyu
Revision: 24442
Changed Files:
U   trunk/doc/admin.texinfo
U   trunk/src/kadmin/cli/kadmin.M
U   trunk/src/kadmin/cli/kadmin.c
U   trunk/src/kadmin/cli/kadmin_ct.ct
U   trunk/src/kadmin/server/kadm_rpc_svc.c
U   trunk/src/kadmin/server/ovsec_kadmd.c
U   trunk/src/kadmin/server/server_stubs.c
U   trunk/src/lib/kadm5/admin.h
U   trunk/src/lib/kadm5/clnt/client_principal.c
U   trunk/src/lib/kadm5/clnt/client_rpc.c
U   trunk/src/lib/kadm5/clnt/libkadm5clnt_mit.exports
U   trunk/src/lib/kadm5/kadm_rpc.h
U   trunk/src/lib/kadm5/kadm_rpc_xdr.c
U   trunk/src/lib/kadm5/srv/libkadm5srv_mit.exports
U   trunk/src/lib/kadm5/srv/svr_principal.c