translate array drop glue using MIR

This fixes leakage on panic with arrays & slices. I am using a C-style
for-loop instead of a pointer-based loop because that would be ugly-er
to implement.

src/test/run-pass/dynamic-drop.rs

@@ -125,6 +125,14 @@ fn union1(a: &Allocator) {
     }
 }
 
+fn array_simple(a: &Allocator) {
+    let _x = [a.alloc(), a.alloc(), a.alloc(), a.alloc()];
+}
+
+fn vec_simple(a: &Allocator) {
+    let _x = vec![a.alloc(), a.alloc(), a.alloc(), a.alloc()];
+}
+
 fn run_test<F>(mut f: F)
     where F: FnMut(&Allocator)
 {
@@ -171,5 +179,8 @@ fn main() {
     run_test(|a| assignment1(a, false));
     run_test(|a| assignment1(a, true));
 
+    run_test(|a| array_simple(a));
+    run_test(|a| vec_simple(a));
+
     run_test_nopanic(|a| union1(a));
 }