Fix regression in colorization of zippy-matched commands

Fix regression in colorization of zippy-matched commands

The patch by Daniel Mehrman from 4.2.pre8 was not properly merged, so
that in XBoard no coloration would take place of ICS commands that were
matched by zippy. (It was using &i as input pointer, rather than &backup.
The XBoard-specific code now has been deleted completely, to remove a
seemingly needless dependence on _WIN32_ of the back-end. Both WB and XB
now use the XBoard method, to only match zippy commands when logged in.