[racket] MysterX poll

If you use MysterX for COM/ActiveX work under Windows --- or if you are
interested in using it --- please drop me a note. 

If no one is using MysterX, then it may go away, because we have
trouble maintaining it.

If you tell me that you're (interested in) using MysterX, please also
let me know which parts you (would) use:

 * The basic COM layer (sections 2.1-2.2 in the MysterX reference)?
 * The event layer (section 2.3 in the MysterX reference)?
 * The ActiveX layer (section 3 in the MysterX reference)?


Depending whether anyone uses MysterX and which parts are used, then it
might get replaced by an `ffi/unsafe/com' library that is implemented
in Racket, that covers the basic COM layer of MysterX, and that also
leverages the FFI to better support calling COM methods directly (e.g.,
with a `define-com-class' form) instead of relying only on IDispatch.