backport r22890 from trunk

backport r22890 from trunk

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 r22890 | ghudson | 2009-10-13 15:43:17 -0400 (Tue, 13 Oct 2009) | 11 lines

 ticket: 6573
 subject: Fix preauth looping in krb5_get_init_creds
 tags: pullup
 target_version: 1.7.1

 In 1.7, krb5_get_init_creds will continue attempting the same built-in
 preauth mechanism (e.g. encrypted timestamp) until the loop counter
 maxes out.  Until the preauth framework can remember not to retry
 built-in mechanisms, only continue with preauth after a PREAUTH_FAILED
 error resulting from optimistic preauth.

ticket: 6573
version_fixed: 1.7.1
status: resolved

git-svn-id: svn://anonsvn.mit.edu/krb5/branches/krb5-1-7@23640 dc483132-0cff-0310-8789-dd5450dbe970