Add option to allow return outside of functions.

Close #288

bin/uglifyjs

@@ -64,6 +64,7 @@ You need to pass an argument to this option to specify the name that your module
     .describe("v", "Verbose")
     .describe("V", "Print version number and exit.")
     .describe("noerr", "Don't throw an error for unknown options in -c, -b or -m.")
+    .describe("bare-returns", "Allow return outside of functions.  Useful when minifying CommonJS modules.")
 
     .alias("p", "prefix")
     .alias("o", "output")
@@ -100,6 +101,7 @@ You need to pass an argument to this option to specify the name that your module
     .boolean("lint")
     .boolean("V")
     .boolean("noerr")
+    .boolean("bare-returns")
 
     .wrap(80)
 
@@ -275,9 +277,10 @@ async.eachLimit(files, 1, function (file, cb) {
             else {
                 try {
                     TOPLEVEL = UglifyJS.parse(code, {
-                        filename   : file,
-                        toplevel   : TOPLEVEL,
-                        expression : ARGS.expr,
+                        filename     : file,
+                        toplevel     : TOPLEVEL,
+                        expression   : ARGS.expr,
+                        bare_returns : ARGS.bare_returns,
                     });
                 } catch(ex) {
                     if (ex instanceof UglifyJS.JS_Parse_Error) {

lib/parse.js

@@ -609,6 +609,7 @@ function parse($TEXT, options) {
         toplevel       : null,
         expression     : false,
         html5_comments : true,
+        bare_returns   : false,
     });
 
     var S = {
@@ -788,7 +789,7 @@ function parse($TEXT, options) {
                 return if_();
 
               case "return":
-                if (S.in_function == 0)
+                if (S.in_function == 0 && !options.bare_returns)
                     croak("'return' outside of function");
                 return new AST_Return({
                     value: ( is("punc", ";")