Update OASIS, crypt_blowfish.c, and enable C compiler optimizations

Hiya,

I noticed in my testing that hashing was slower compared to using an equivalent library in python.  After a little digging it turns out that the reason for the slowdown was simply because compiler optimizations were not run on the C code in ocaml-safepass.  After switching to a version of OASIS that supports using C compiler flags, the hashing is the same speed as of the python bindings and a straight C implementation.