core: Add binary_search and binary_search_elem methods to slices.

These are like the existing bsearch methods but if the search fails,
it returns the next insertion point.

The new `binary_search` returns a `BinarySearchResult` that is either
`Found` or `NotFound`. For convenience, the `found` and `not_found`
methods convert to `Option`, ala `Result`.

Deprecate bsearch and bsearch_elem.

src/libcoretest/lib.rs

@@ -28,4 +28,5 @@ mod option;
 mod ptr;
 mod raw;
 mod result;
+mod slice;
 mod tuple;

src/libcoretest/slice.rs

@@ -0,0 +1,35 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::slice::{Found, NotFound};
+
+#[test]
+fn binary_search_not_found() {
+    let b = [1i, 2, 4, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&6)) == Found(3));
+    let b = [1i, 2, 4, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&5)) == NotFound(3));
+    let b = [1i, 2, 4, 6, 7, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&6)) == Found(3));
+    let b = [1i, 2, 4, 6, 7, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&5)) == NotFound(3));
+    let b = [1i, 2, 4, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&8)) == Found(4));
+    let b = [1i, 2, 4, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&7)) == NotFound(4));
+    let b = [1i, 2, 4, 6, 7, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&8)) == Found(5));
+    let b = [1i, 2, 4, 5, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&7)) == NotFound(5));
+    let b = [1i, 2, 4, 5, 6, 8, 9];
+    assert!(b.binary_search(|v| v.cmp(&0)) == NotFound(0));
+    let b = [1i, 2, 4, 5, 6, 8];
+    assert!(b.binary_search(|v| v.cmp(&9)) == NotFound(6));
+}