semi-major change checked in

[Christopher Faylor]

I just checked in a minor change to the way that file handles are
inherited.  It had major effects on most of the sources in
winsup/cygwin fdtab has now become cygheap->fdtab.

The impetus for this change is so that I can actually get vfork
working.  I think I will still play it safe and keep vfork turned
off for 1.3.0 but I will turn it on for 1.3.1.

I also checked in other things that have been accumulating in my
sandbox, like the passwd_sem removal.

I need to remove group_sem at some point, too, unless someone
beats me to it.

cgf