Parenthesize unary move exprs in prettyprinter

Closes #3220

src/libsyntax/print/pprust.rs

@@ -1234,7 +1234,12 @@ fn print_field(s: ps, field: ast::field) {
         print_block(s, blk);
       }
       ast::expr_copy(e) => { word_space(s, ~"copy"); print_expr(s, e); }
-      ast::expr_unary_move(e) => { word_space(s, ~"move"); print_expr(s, e); }
+      ast::expr_unary_move(e) => {
+          popen(s);
+          word_space(s, ~"move");
+          print_expr(s, e);
+          pclose(s);
+      }
       ast::expr_move(lhs, rhs) => {
         print_expr(s, lhs);
         space(s.s);

src/test/run-pass/issue-3220.rs

@@ -0,0 +1,7 @@
+struct thing { x: int; new () { self.x = 0; } drop { } }
+impl thing { fn f(self) {} }
+
+fn main() {
+    let z = thing();
+    (move z).f();
+}