improve process.exit() workaround (#2741)

- use public API
- fix issue with Node.js 0.10 on WIndows

bin/uglifyjs

@@ -3,11 +3,7 @@
 
 "use strict";
 
-// workaround for tty output truncation upon process.exit()
-[process.stdout, process.stderr].forEach(function(stream){
-    if (stream._handle && stream._handle.setBlocking)
-        stream._handle.setBlocking(true);
-});
+require("../tools/exit");
 
 var fs = require("fs");
 var info = require("../package.json");