The MIT krb5 and Heimdal implementations of

The MIT krb5 and Heimdal implementations of
gss_krb5_export_lucid_sec_context error on version arguments other
than 1, so the version negotiation described in the function
documentation would not be backward-compatible.  Change the docs so
that the caller can assume the returned structure is of the requested
version, but the caller will be responsible for retrying with lower
version numbers on error.  (Unfortunately, Heimdal and MIT return
different error codes, and MIT's is in a currently-unpublished header,
so we can't document the error code for unknown versions.)

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24903 dc483132-0cff-0310-8789-dd5450dbe970