First cut at git port to Cygwin

I have made a first cut at a git port to Cygwin. It looks like the "git-diff-tree -p" problem has been resolved independently, or at least I can't reproduce it on a fresh Cygwin install (running on XP Home), but I have added support for running without the IPv6 and the getaddrinfo() API.

There are still funnies. In particular, Cygwin and Samba handle symlinks differently, so you can't trivially share a repository via Samba. Linus' "symbolic refs" changes should eventually take care of that.

Another funny which I haven't been able to figure out yet is that 'gitk' 
scrunches all its output up into a few pixels at the top of the window. 
  If I maximize the window, I can manually resize most of the panes and 
the output looks correct, but the highlighted text in the top panes show 
up in black on a really really dark blue background and is thus illegible.

I have set up a git-on-Cygwin temporary tree at:

http://www.kernel.org/pub/scm/git/git-cygwin.git

	-hpa