[krbdev.mit.edu #6210] pa_sam leaks parts of krb5_sam_challenge

[Greg Hudson via RT]

I handled the error cases but appear to have missed the main
(successful) code path.  Reopening this ticket.

Also, there is some ugly stuff going on in that function where
structures are partially constructed with allocated data and not freed,
and at least one case where a structure does a shallow copy of allocated
data from another structure and neither is freed.  I will need to do
some more careful analysis.