(WIP) Small fixes in chalkification
Small fixes around region constraints and builtin impls. There are still some type inference errors, for example the following code errors out:
```rust
fn main() {
let mut x: Vec<i32> = Vec::new();
// ^^^^^^^^ cannot infer type for `std::vec::Vec<_>`
}
```
but explicitly specifying `Vec::<i32>::new` works.
With these few fixes, the following code now passes type-checking:
```rust
fn main() {
let mut x: Vec<i32> = Vec::<i32>::new();
x.push(5);
println!("{:?}", x);
}
```
I also fixed the implied bounds bug as discussed on Zulip and in https://github.com/rust-lang-nursery/chalk/pull/206
cc @tmandry
r? @nikomatsakis
c7b5f4d0f7