provide a `SpecExtend` trait for `Vec<T>` The discussion is [here](https://internals.rust-lang.org/t/append-vec-to-binaryheap/15209/3)
provide a `SpecExtend` trait for `Vec<T>`
The discussion is [here](https://internals.rust-lang.org/t/append-vec-to-binaryheap/15209/3)

aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust