/cygdrive improvements

[Christopher Faylor]

I've just made some changes to cygwin.

I've added opendir, readdir, telldir, etc.  methods to the fhandler
class.

I also implemented /cygdrive as a special "device" in cygwin.  Cygdrive
inherits most of its methods from fhandler_disk_file except for the opendir
ones.

I've implemented the directory handling methods for cygdrive so that you
can now do this:

    % ls /cygdrive
    a   c  d  e

This allows completion in shells like zsh.

The only thing wrong with this currently is that zsh times out trying to
read the floppy drive the first time.

This is probably not the most elegant way of doing things.  We maybe
should have another directory handling layer and yada, yada.  If you've
been reading this mailing list for any length of time, you know all of
the arguments.

I just thought it would be fun to implement things this way and it was.
It wasn't even that ugly.

Anyway, I'll probably let this percolate for a while and then release
1.3.6.  I'm sure that I have screwed up something that needs some
attention but, for now, I'm going to bed to dream of turkey.

cgf