fixes #259: don't unnecessarily quote object properties when --screw-ie8

lib/output.js

@@ -54,13 +54,13 @@ function OutputStream(options) {
         inline_script : false,
         width         : 80,
         max_line_len  : 32000,
-        ie_proof      : true,
         beautify      : false,
         source_map    : null,
         bracketize    : false,
         semicolons    : true,
         comments      : false,
         preserve_line : false,
+        screw_ie8     : false,
         negate_iife   : !(options && options.beautify),
     }, true);
 
@@ -761,7 +761,7 @@ function OutputStream(options) {
         if (!self.body)
             return output.force_semicolon();
         if (self.body instanceof AST_Do
-            && output.option("ie_proof")) {
+            && !output.option("screw_ie8")) {
             // https://github.com/mishoo/UglifyJS/issues/#issue/57 IE
             // croaks with "syntax error" on code like this: if (foo)
             // do ... while(cond); else ...  we need block brackets
@@ -1048,10 +1048,10 @@ function OutputStream(options) {
                     && +key + "" == key)
                    && parseFloat(key) >= 0) {
             output.print(make_num(key));
-        } else if (!is_identifier(key)) {
-            output.print_string(key);
-        } else {
+        } else if (RESERVED_WORDS(key) ? output.option("screw_ie8") : is_identifier_string(key)) {
             output.print_name(key);
+        } else {
+            output.print_string(key);
         }
         output.colon();
         self.value.print(output);