Replacing libspf2 with libspf

Some people have mailed me asking for how I patched to use libspf 
instead of libspf2 (which I believe is seriously broken).

Here it is: http://www.ricky-chan.co.uk/exim/

I based it on Tom's code but replaced calls to libspf2 to libspf.  works 
will for me but haven't tested the smtp_comment_headers and the other 3 
much as I don't use them but I choose what I thought as similar 
functions/variables as used in libspf.

I think explain is set to NULL, as I never bother to build_explain as 
shown in API for libspf, but I haven't a use for it.  Submission for 
ideas, fixes etc.. are welcome.

Thanks again to Tom for his great work.

Ricky