improve parenthesis emission (#2196)

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

test/compress/sequences.js

@@ -176,6 +176,11 @@ for_sequences: {
         // 4
         x = (foo in bar);
         for (y = 5; false;);
+        // 5
+        x = function() {
+            foo in bar;
+        };
+        for (y = 5; false;);
     }
     expect: {
         // 1
@@ -188,6 +193,10 @@ for_sequences: {
         // 4
         x = (foo in bar);
         for (y = 5; false;);
+        // 5
+        for (x = function() {
+            foo in bar;
+        }, y = 5; false;);
     }
 }