Can't assign 0 to function pointer

[Thierry Delisle]

This code crashes the compiler:

int main() {
	int (*foo)(int) = 0;
}

[a3moss]

There's a commented-out line 808 in prelude.cf, that looks like it would do the right thing:
// forall( ftype FT ) void ?{}( FT * *, zero_t );

It looks like Rob put it in in commit 0b150ecc back in late May -- Rob, do you remember why it's commented out?

[Rob Schluntz <rschlunt@…>]

In 969ee0d:

conversion of zero_t to function type does not require tuple specialization [fixes #17]

[Rob Schluntz]

That's an interesting observation. I'm not sure why it's commented, but it might be necessary for assertions?

In any case, I've handled the zero_t case separately for tuple specialization, since zero_t is special.