r16952: New derive DES salt code and Krb5 keytab generation

r16952: New derive DES salt code and Krb5 keytab generation

Major points of interest:

* Figure the DES salt based on the domain functional level
  and UPN (if present and applicable)
* Only deal with the DES-CBC-MD5, DES-CBC-CRC, and RC4-HMAC
  keys
* Remove all the case permutations in the keytab entry
  generation (to be partially re-added only if necessary).
* Generate keytab entries based on the existing SPN values
  in AD

The resulting keytab looks like:

ktutil:  list -e
slot KVNO Principal
---- ---- ---------------------------------------------------------------------
   1    6 host/suse10.plainjoe.org@COLOR.PLAINJOE.ORG (DES cbc mode with CRC-32)
   2    6 host/suse10.plainjoe.org@COLOR.PLAINJOE.ORG (DES cbc mode with RSA-MD5)
   3    6 host/suse10.plainjoe.org@COLOR.PLAINJOE.ORG (ArcFour with HMAC/md5)
   4    6           host/suse10@COLOR.PLAINJOE.ORG (DES cbc mode with CRC-32)
   5    6           host/suse10@COLOR.PLAINJOE.ORG (DES cbc mode with RSA-MD5)
   6    6           host/suse10@COLOR.PLAINJOE.ORG (ArcFour with HMAC/md5)
   7    6               suse10$@COLOR.PLAINJOE.ORG (DES cbc mode with CRC-32)
   8    6               suse10$@COLOR.PLAINJOE.ORG (DES cbc mode with RSA-MD5)
   9    6               suse10$@COLOR.PLAINJOE.ORG (ArcFour with HMAC/md5)

The list entries are the two basic SPN values (host/NetBIOSName & host/dNSHostName)
and the sAMAccountName value.  The UPN will be added as well if the machine has
one. This fixes 'kinit -k'.

Tested keytab using mod_auth_krb and MIT's telnet.  ads_verify_ticket()
continues to work with RC4-HMAC and DES keys.