r11196: Clean up memory leaks (pointed out by vl), and handle the case where

r11196: Clean up memory leaks (pointed out by vl), and handle the case where
the client doesn't guess correctly on the mech to use.  It must back
off and try the mech the server selected from the list.

I'm not particularly attached to our SPNEGO parser, so while I can't
easily use the SPNEGO application logic in Heimdal, I'm going to look
closely at using the asn1 routines to avoid some pain here.

Andrew Bartlett