Fix matching of rvalues with destructors

Fixes #4542.

src/test/run-pass/match-vec-rvalue.rs

@@ -0,0 +1,12 @@
+// Tests that matching rvalues with drops does not crash.
+
+fn main() {
+    match ~[1, 2, 3] {
+        x => {
+            assert_eq!(x.len(), 3);
+            assert_eq!(x[0], 1);
+            assert_eq!(x[1], 2);
+            assert_eq!(x[2], 3);
+        }
+    }
+}