Fixed writecontents for files that don't have a flush method

fs/base.py

@@ -570,6 +570,7 @@ class FS(object):
                     chunk = data.read(1024*512)
             else:
                 f.write(data)
+            if hasattr(f, 'flush'):
                 f.flush()
         finally:
             if f is not None: