accept_sec_context.c (krb5_gss_accept_sec_context): Reorganized error

accept_sec_context.c (krb5_gss_accept_sec_context): Reorganized error
	handling code to be more compact (and correct!).  If an error occurs
	while we are doing mutual authentication, send an KRB_ERROR message
	back to the client, so that it knows what is going on.  (This is
	specified by RFC 1964; we just weren't implementing this previously.)

delete_sec_context.c (krb5_gss_delete_sec_context): Check to make sure
	pointers in the context are non-zero before freeing them.

init_sec_context.c (krb5_gss_init_sec_context): If the server sends a
	KRB_ERROR message, decode it and return an appropriate minor status
	error code.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@10094 dc483132-0cff-0310-8789-dd5450dbe970