pull up r18858 from trunk

pull up r18858 from trunk

 r18858@cathode-dark-space:  coffman | 2006-11-21 09:37:11 -0500
 ticket: new
 subject: free error message when freeing context
 Target_Version: 1.6
 Tags: pullup

 Call krb5_clear_error_message() to free any allocated error message
 before freeing the context.

 The condition that triggered this was a plugin library which fails to
 load because of unresolved references.  It appears dlopen() on Linux
 leaks four bytes for each failing library in this situation.

ticket: 4841
version_fixed: 1.6
component: krb5-libs

git-svn-id: svn://anonsvn.mit.edu/krb5/branches/krb5-1-6@18884 dc483132-0cff-0310-8789-dd5450dbe970