Calling psconfig with non-existing option (e.g. -build) shouldn't unset PATH

[Sebastian Jester]

Sometimes I mistype or misguess an option to psconfig, e.g.

psconfig -build

After issuing that command, PATH is empty, and the shell I'm in has become useless. While that's probably mostly only a nuisance, maybe worse things could happen by accident, and it always breaks the flow of whatever one is doing at the time. Ideally, psconfig would complain about invalid options being passed.