Add tests for macro-based impls

[Manishearth]

A lot of impls for primitives in libcore are done via macros, in lieu of variadic generics. This is done for tuples, function pointers, and arrays.

However, tweaking these macros can sometimes lead to regressions like these (caused by this tweak).

We should have some run-pass tests that ensure that the relevant traits are indeed implemented. Something like

#[derive(Copy,Clone, Eq,PartialEq,Hash,Ord,Debug)]
struct Fn {
    fn0: fn(),
    fn1: fn(u8),
    fn2: fn(u8, u8),
    ...
    fn12: fn(u8, u8, u8 ....)
}

for fn, and similar for the other macro-impld primitives.

[Manishearth]

@apasel422 Interested in working on this?

[apasel422]

@Manishearth Sure!