Set a timeout on "Do you want"-prompts

If we need too long to respond gpg thinks it's agent died and tries to
restart it. This doesn't work with split-gpg and is anyway not what we
want.

This also has the advantage that if a scripts tries to to a bunch of
operations without waiting for success all the windows can be cleaned up
by just waiting for the timeout.

splitgpg2/__init__.py

@@ -330,7 +330,7 @@ def request_timer(self, name):
             short_msg,
             'for the next {}s'.format(delay) if delay is not None else '')
         if subprocess.call(['zenity', '--question', '--title', short_msg,
-                            '--text', question]) != 0:
+                            '--text', question, '--timeout', '30']) != 0:
             raise Filtered
 
         self.notify('command {} allowed'.format(name))