Patch inspired by one from Daniel Silverstone in Debian bug #229232:

Patch inspired by one from Daniel Silverstone in Debian bug #229232:

We now have an option where a remote window title query returns a well-formed
response containing the empty string. This should keep stop any server-side
application that was expecting a response from hanging, while not permitting
the response to be influenced by an attacker.

We also retain the ability to stay schtum. The existing checkbox has thus
grown into a set of radio buttons.

I've changed the default to the "empty string" response, even in the backward-
compatibility mode of loading old settings, which is a change in behaviour;
any users who want the old behaviour back will have to explicitly select it. I
think this is probably the Right Thing. (The only drawback I can think of is
that an attacker could still potentially use the relevant fixed strings for
mischief, but we already have other, similar reports.)

[originally from svn r7043]