Integer type inference doesn't check trait implementations

[sfackler]

Ideally something like this would work, but it currently doesn't:

trait Foo {}

impl Foo for i32 {}

struct Baz;

fn foo<F: Foo>(f: F) {}

fn main() {
    foo(10);
}

test.rs:11:5: 11:8 error: cannot determine the type of this integer; add a suffix to specify the type explicitly
test.rs:11     foo(10);
               ^~~
test.rs:11:5: 11:8 error: failed to find an implementation of trait Foo for int
test.rs:11     foo(10);
               ^~~

[sfackler]

This works now, yay trait reform!