_ffi syntax

[Stephen Weeks]

> Why is it that a semicolon is required at the end of an _ffi.  I guess I have
> the same question about _prim.  I'm confused syntactically what is going  on.
> I  would  have  expected this to just be a declaration, and probably have the
> `_ffi' replace `val'.

For no good reason that I can remember, I decided to make _ffi and _prim
expressions instead of declarations.  Given that choice, the ; was required to
avoid a shift/reduce conflict.  Making it a declaration seems like a fine idea
to me, although I'd have to investigate in more detail to be sure.