pull up r19526 from trunk

pull up r19526 from trunk

 r19526@cathode-dark-space:  tlyu | 2007-04-25 17:19:07 -0400
 ticket: new
 target_version: 1.6.2
 tags: pullup
 subject: race condition in referrals fallback

 	* src/lib/krb5/krb/gc_frm_kdc.c (krb5_get_cred_from_kdc_opt):
 	During referrals fallback, set *tgts to NULL after freeing.  This
 	avoids returning a pointer to freed memory when the first call to
 	do_traversal() obtains some TGTs and the subsequent
 	krb5_cc_retrieve_cred() of the final-hop TGT succeeds (due to some
 	other thread or process storing that TGT into the ccache), causing
 	second do_traversal() call (which would re-initialize *tgts) to
 	not execute.  Race condition found during KfW-3.2 testing.

ticket: 5546
version_fixed: 1.6.2

git-svn-id: svn://anonsvn.mit.edu/krb5/branches/krb5-1-6@19528 dc483132-0cff-0310-8789-dd5450dbe970