wrap tempfile.mkstemp to work on windows

The path returned by tempfile.mkstemp is encoded in system locale,
since we need to pass it through rpc, we need it to be encoded in UTF-8

utils/__init__.py

@@ -7,6 +7,8 @@ import urllib2
 import uuid
 import logging
 import json
+import tempfile
+import locale
 
 from django.contrib.sites.models import RequestSite
 from django.db import IntegrityError
@@ -855,5 +857,15 @@ def redirect_to_login(request):
     tup = login_url, redirect_field_name, path
     return HttpResponseRedirect('%s?%s=%s' % tup)
 
+def mkstemp():
+    '''Returns (fd, filepath), the same as tempfile.mkstemp, except the
+    filepath is encoded in UTF-8
+
+    '''
+    fd, path = tempfile.mkstemp()
+    system_encoding = locale.getdefaultlocale()[1]
+    path_utf8 = path.decode(system_encoding).encode('UTF-8')
+    return fd, path_utf8
+
 # Move to here to avoid circular import.
 from base.models import FileContributors, UserStarredFiles, DirFilesLastModifiedInfo, FileLastModifiedInfo