Revert c1423a8eea706f5b0d043878f4c9a00b27ebcb6d

And fix a buglet in lib/krb5/plugin.c: stop invoking plugins as soon as
one returns anything other than KRB5_PLUGIN_NO_HANDLE.
A few more lib/krb5/plugin.c fixes from Love
Fix master (lib/krb5 warnings)
Quiet a warning in test_plugin.c