Fix return code and unset fields

Patch sent by Wolfgang Breyha to the spf-devel mailing list.
Fixes from ddave1's fork

https://github.com/ddave1/libspf2/commit/8bdce2df720028038e931e5a04e3d6ed6a8c883b
Let the code compile
Fix handling of email addresses in query_rcptto

From Florian Forster to the spf-devel mailing list:
http://www.gossamer-threads.com/lists/spf/devel/36083
Fix spacing and typo
Always retry after errors on SPF record lookup

This is meant as a protection against old/buggy/crappy DNS servers
which return errors when they receive SPF record queries.
Fix indentation from Andre Nathan.