I have no idea why this was here. It makes no sense. If you're trying
to find out if something is a directory, why wouldn't you be allowed to
ask that about a FIFO? :^)
Thanks to Brandon for spotting this!
Also, while we're here, cache the directory state in a bool member so
we don't have to keep fetching inode metadata when checking this
repeatedly. This is important since sys$read() now calls it.