libspf now handles SPF RRs in linux (libresolv)

Hi,

I noticed that libspf2 wasn't using SPF RRs.  When I investigated it was due to "ns_t_spf" not being handled upon reception of the DNS response.  The fix for this is trivial as mst of the hard work in getting SPF RRs included was already done.

I also added a small change into the cache so that SPF RRs are treated the same as TXT RRs.

Thanks,
ddave1

P.S.  I'm new to git, when I tried to add your repo as a remote it wouldn't work.  I need to use the http link due to firewall restrictions but I get a 403 when I try to fetch.