Add an option to wrap IIFEs in parenthesis

For #1307.

lib/output.js

@@ -67,7 +67,8 @@ function OutputStream(options) {
         screw_ie8        : true,
         preamble         : null,
         quote_style      : 0,
-        keep_quoted_props: false
+        keep_quoted_props: false,
+        wrap_iife        : false,
     }, true);
 
     // Convert comment option to RegExp if neccessary and set up comments filter
@@ -552,7 +553,17 @@ function OutputStream(options) {
     // a function expression needs parens around it when it's provably
     // the first token to appear in a statement.
     PARENS(AST_Function, function(output){
-        return first_in_statement(output);
+        if (first_in_statement(output)) {
+            return true;
+        }
+
+        if (output.option('wrap_iife')) {
+            var p = output.parent();
+            console.log()
+            return p instanceof AST_Call && p.expression === this;
+        }
+
+        return false;
     });
 
     // same goes for an object literal, because otherwise it would be