Add parens, as needed, around else-if conditions.

src/comp/syntax/print/pprust.rs

@@ -625,7 +625,7 @@ fn print_if(s: ps, test: @ast::expr, blk: ast::blk,
                 cbox(s, indent_unit - 1u);
                 ibox(s, 0u);
                 word(s.s, " else if ");
-                print_expr(s, i);
+                print_maybe_parens_discrim(s, i);
                 space(s.s);
                 print_block(s, t);
                 do_else(s, e);

src/test/run-pass/wierd-exprs.rs

@@ -21,8 +21,15 @@ fn what() {
 }
 
 fn zombiejesus() {
-    do  { while (ret) { if (ret) { alt (ret) { _ { ret ? ret : ret } } } } }
-        while ret
+    do  {
+        while (ret) {
+            if (ret) {
+                alt (ret) { _ { ret ? ret : ret } };
+            } else if (ret) {
+                ret;
+            }
+        }
+    } while ret
 }
 
 fn notsure() {