Add --screw-ie option

For now the implication is that UglifyJS will not leak a function
expression's name in the surrounding scope (IE < 9 does that).

(ref. mishoo/UglifyJS#485)

bin/uglifyjs

@@ -21,6 +21,7 @@ mangling you need to use `-c` and `-m`.\
     .describe("source-map-root", "The path to the original source to be included in the source map.")
     .describe("source-map-url", "The path to the source map to be added in //@ sourceMappingURL.  Defaults to the value passed with --source-map.")
     .describe("in-source-map", "Input source map, useful if you're compressing JS that was generated from some other original code.")
+    .describe("screw-ie", "Pass this flag if you don't care about full compliance with Internet Explorer quirks (by default UglifyJS will try to be IE-proof).")
     .describe("p", "Skip prefix for original filenames that appear in source maps. \
 For example -p 3 will drop 3 directories from file names and ensure they are relative paths.")
     .describe("o", "Output file (default STDOUT).")
@@ -71,6 +72,7 @@ You need to pass an argument to this option to specify the name that your module
     .string("d")
     .string("comments")
     .string("wrap")
+    .boolean("screw-ie")
     .boolean("export-all")
     .boolean("self")
     .boolean("v")
@@ -246,7 +248,7 @@ var SCOPE_IS_NEEDED = COMPRESS || MANGLE || ARGS.lint;
 
 if (SCOPE_IS_NEEDED) {
     time_it("scope", function(){
-        TOPLEVEL.figure_out_scope();
+        TOPLEVEL.figure_out_scope({ screw_ie: ARGS.screw_ie });
         if (ARGS.lint) {
             TOPLEVEL.scope_warnings();
         }
@@ -261,7 +263,7 @@ if (COMPRESS) {
 
 if (SCOPE_IS_NEEDED) {
     time_it("scope", function(){
-        TOPLEVEL.figure_out_scope();
+        TOPLEVEL.figure_out_scope({ screw_ie: ARGS.screw_ie });
         if (MANGLE) {
             TOPLEVEL.compute_char_frequency(MANGLE);
         }

lib/scope.js

@@ -67,7 +67,10 @@ SymbolDef.prototype = {
     }
 };
 
-AST_Toplevel.DEFMETHOD("figure_out_scope", function(){
+AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
+    options = defaults(options, {
+        screw_ie: false
+    });
     // This does what ast_add_scope did in UglifyJS v1.
     //
     // Part of it could be done at parse time, but it would complicate
@@ -121,14 +124,16 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(){
             node.init_scope_vars();
         }
         if (node instanceof AST_SymbolLambda) {
-            //scope.def_function(node);
-            //
+            if (options.screw_ie) {
+                scope.def_function(node);
+            } else {
                 // https://github.com/mishoo/UglifyJS2/issues/24 — MSIE
                 // leaks function expression names into the containing
                 // scope.  Don't like this fix but seems we can't do any
                 // better.  IE: please die. Please!
                 (node.scope = scope.parent_scope).def_function(node);
             }
+        }
         else if (node instanceof AST_SymbolDefun) {
             // Careful here, the scope where this should be defined is
             // the parent scope.  The reason is that we enter a new