stdlib: Add missing unsafe.rs. Puts out burning tinderbox.

src/lib/unsafe.rs

@@ -0,0 +1,9 @@
+// Unsafe operations.
+
+native "rust-intrinsic" mod rusti {
+    fn cast[T,U](&T src) -> U;
+}
+
+// Casts the value at `src` to U. The two types must have the same length.
+fn reinterpret_cast[T,U](&T src) -> U { ret rusti::cast(src); }
+