Fix reversed mouse wheel on Win32GDI...

From MSDN:
A positive value indicates that the wheel was rotated forward
away from the user; a negative value indicates that the wheel
was rotated backward, toward the user.

Fixes bug 143.

However, this re-opens the confusion around request 75...
nigel and DigitalMan should take a look at this more closely
in rc2 (or an updated nightly).

src/conio/win32gdi.c

@@ -485,7 +485,7 @@ gdi_handle_mouse_button(LPARAM lParam, int event)
 static LRESULT
 gdi_handle_mouse_wheel(int16_t distance, LPARAM lParam)
 {
-	if (distance < 0) // Forward
+	if (distance > 0) // Forward
 		ciomouse_gotevent(CIOLIB_BUTTON_PRESS(4), -1, -1 ,-1 ,-1);
 	else
 		ciomouse_gotevent(CIOLIB_BUTTON_PRESS(5), -1, -1 ,-1 ,-1);