[jhc] darcs patch: HsFFI.h is not in C include path.

Sun Jun 21 19:27:03 PDT 2009 coreyoconnor@gmail.com * HsFFI.h is not in C include path. Unable to compile due to missing HsFFI.h. I think the intention is to use the include file it the "data" folder. Updating Makefile accordingly.