Merge pull request rust-lang#273 from RalfJung/ref

Test that &* of a dangling (and even unaligned) ptr is okay

Author: oli-obk

tests/run-pass/ref-invalid-ptr.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let x = 2usize as *const u32;
+    let _y = unsafe { &*x as *const u32 };
+
+    let x = 0usize as *const u32;
+    let _y = unsafe { &*x as *const u32 };
+}