Adding include files copied from a post-build version of
nacl-20110221.

ed255519 now compiles (doesn't link) with: "gcc *.c -Inacl_includes"

With the same command, curve25519 almost compiles but can't find
crypto_scalarmult.h.  That's not in nacl or supercop, so I'm not sure
where it's supposed to come from.