Don't leak PKINIT CMS signed data certs and CRLs

The stacks of certificates and CRLs that we retrieve from CMS objects
include newly-owned references to the certificates and CRLs, so when we
go to free them, we need to remember to free those.

[ghudson@mit.edu: minor formatting change; removed unrelated style fix]
Fix minor leaks in klist

When walking the cache, if we skip a cred because it's a config entry,
make sure to free it.  Also free the result of krb5_cc_get_principal.
Based on a patch from Nalin Dahyabhai.
Fix a leak when parsing PKINIT cert SANs with NSS

When retrieving the list of a certificate's subjectAltName values, we
weren't freeing some of the temporary memory we used.