pull up 21993 from trunk

pull up 21993 from trunk

 Subject: Implement TGS authenticator subkey usage
 ticket: 6393
 tags: enhancement

 Implement support for use of a subkey in the TGS req.  This is needed
 by FAST TGS support.  The interface to krb5_send_tgs changed in order
 to gain a subkey output parameter.  Since this is a private interface
 it was renamed to krb5int_send_tgs and removed from the export list.

 * send_tgs.c: generate a subkey and return to caller
 * decode_kdc_rep.c: Use subkey keyusage
 * gc_via_tkt.c: pass in subkey to decode_kdc_rep
 * send_tgs.c: use subkey for encrypting authorization data

ticket: 6393
version_fixed: 1.7

git-svn-id: svn://anonsvn.mit.edu/krb5/branches/krb5-1-7@22201 dc483132-0cff-0310-8789-dd5450dbe970