atomic write wallet file

lib/wallet.py

@@ -136,8 +136,9 @@ class WalletStorage(object):
     def write(self):
         assert not threading.currentThread().isDaemon()
         s = json.dumps(self.data, indent=4, sort_keys=True)
-        with open(self.path,"w") as f:
+        with open(self.path + '.tmp', "w") as f:
             f.write(s)
+        os.rename(self.path + '.tmp', self.path)
         if 'ANDROID_DATA' not in os.environ:
             import stat
             os.chmod(self.path,stat.S_IREAD | stat.S_IWRITE)