fixed different use of engine option compared to Polyglot

fixed different use of engine option compared to Polyglot

it turns out the new Polyglot uses a sightly different version of the GUI->engine option command than the one I proposed (and implemented in XBoard; Michel sneaked in an '=' sign between the NAME and VALUE of the option, to allow for more unambiguous parsing.

I guess in principle this is a good idea, so I adapted XBoard to Polyglot rather than the other way around. The result is that there are canges in xboard.c, and the documentation.

I noticed that I unjustly had internationalized the option strings to be send to the engine in xoptions.c; this was of course nonsense, as this was WB protocol. So I undid that too.