handle kdb stash being a keytab
    
    In krb5 1.7 and later, the stash file (/var/kerberos/krb5kdc/.k5.$REALM
    on Fedora) is created in the regular keytab format instead of the older
    less-portable one.  Based from comments and code in kt_file.c, here's a
    change to try to recognize that case (the file starts with a magic
    number) and read the master key from Python.
    
    The KDC will still read either format, so I left the bits that set
    things up on replicas alone (advice appreciated).  The patch works as
    expected on my 64-bit box, both on RHEL5 (krb5 1.6.1 with a traditional
    stash file) and on Raw Hide (krb5 1.7 with a keytab).
    
    Backported from IPA v2 patch submitted by Nalin Dahyabhai <nalin@redhat.com>