add a workaround for EPERM issue on windows

Derived from @korto's fix:
https://github.com/rlidwka/sinopia/issues/67#issuecomment-44782521

lib/local-fs.js

@@ -20,12 +20,35 @@ try {
 	}
 }
 
+function tempFile(str) {
+	return str + '.tmp' + String(Math.random()).substr(2)
+}
+
+function renameTmp(src, dst, _cb) {
+	function cb(err) {
+		if (err) fs.unlink(src)
+		_cb(err)
+	}
+
+	if (process.platform !== 'win32') {
+		return fs.rename(src, dst, cb)
+	}
+
+	// windows can't remove opened file,
+	// but it seem to be able to rename it
+	var tmp = tempFile(dst)
+	fs.rename(dst, tmp, function(err) {
+		fs.rename(src, dst, cb)
+		if (!err) fs.unlink(tmp)
+	})
+}
+
 function write(dest, data, cb) {
 	var safe_write = function(cb) {
-		var tmpname = dest + '.tmp' + String(Math.random()).substr(2)
+		var tmpname = tempFile(dest)
 		fs.writeFile(tmpname, data, function(err) {
 			if (err) return cb(err)
-			return fs.rename(tmpname, dest, cb)
+			renameTmp(tmpname, dest, cb)
 		})
 	}
 
@@ -60,7 +83,7 @@ function write_stream(name) {
 		stream.done = function() {
 			function onend() {
 				file.on('close', function() {
-					fs.rename(tmpname, name, function(err) {
+					renameTmp(tmpname, name, function(err) {
 						if (err) {
 							stream.emit('error', err)
 						} else {