plugins XEP-0234, file: use of SatFile for writing too

src/plugins/plugin_misc_file.py

@@ -65,6 +65,12 @@ class SatFile(object):
         self._file.close()
         self.host.removeProgressCb(self.uid, self.profile)
 
+    def flush(self):
+        self._file.flush()
+
+    def write(self, buf):
+        self._file.write(buf)
+
     def read(self, size=-1):
         read = self._file.read(size)
         if not read: