I just added 3 new options on which I have somewhat mixed fealings; their only purpose is basically to wreck proper (documented) operation of XBoard. They can be needed, however to prrovide work-arounds for non-compliant engines. In particular, that silly stuff with SIGINT causes problems running Windows binaries of engines under wine: normally SIGINT would kill the engine process, of course, and the protocol specs recomend either to let the engine suppress sending of it by announcing "feature sigint=0" at startup, or ignore SIGINT. Problem is that under wine, engines that ignore sigint die anyway when they receive it. This should be considered a wine bug, but it is very damaging to the usefulness of XBoard, as most engines are only availableasWindows binaries.
So I needed an option for the user to turn off sigint even when the engine does not do it, and I figured it was more versatile to then allow the user to specify or overrule any engine feature. But of course that offers the user a powerful tool to completely wreck the protocol. This is especially dangerous since the option changing the feature defaults is now implemented as persistent; perhaps we should configure XBoard such that the /etc/xboard.conf resets the option to an empty string _after_ having read the user settings file, so that people can only enable the persistence by first removing that line from the master settings file.
