improve parenthesis emission (#2196)

- eliminate `throw` usages
- suppress extraneous parenthesis
  - `new function() {foo.bar()}.baz`
  - `for (function() { "foo" in bar; };;);`

lib/compress.js

@@ -1201,7 +1201,7 @@ merge(Compressor.prototype, {
                     if (stat instanceof AST_For && !(stat.init instanceof AST_Definitions)) {
                         var abort = false;
                         prev.body.walk(new TreeWalker(function(node) {
-                            if (abort) return true;
+                            if (abort || node instanceof AST_Scope) return true;
                             if (node instanceof AST_Binary && node.operator == "in") {
                                 abort = true;
                                 return true;