Make klog_vsyslog() public?

[Greg Hudson]

You can use com_err or com_err_va to log from a plugin; there's a
com_err hook which will convert those into KDC logs.  This is probably
better than linking against libkadm5srv.

That said, I'll probably take this patch, since we already export
krb5_klog_syslog and I think variable-argument interfaces should
generally be paired with va_arg versions.  As a technical note, your
patch seems to be missing changes to the libkadm5clnt and libkadm5srv
export lists.