sftp breakage on Win32

[Matt Lavin]

After catching up with bzr.dev on my Windows machine I ran into the 
following problem using sftp on Windows.  To work around the issue I 
just removed the 'close_fds' argument, but I doubt that it the best 
solution.  I checked the Python docs and it doesn't mention that the 
argument is not supported on Windows.

[ 9192] Wed 11:57:33.285 ERROR: exceptions.ValueError: close_fds is not 
supported on Windows platforms
  at C:\Python24\lib\subprocess.py line 512
  in __init__
Traceback (most recent call last):
  File "C:\Python24\Lib\site-packages\bzrlib\commands.py", line 557, in 
run_bzr_catch_errors
    return run_bzr(argv)
  File "C:\Python24\Lib\site-packages\bzrlib\commands.py", line 520, in 
run_bzr
    ret = cmd_obj.run_argv(argv)
  File "C:\Python24\Lib\site-packages\bzrlib\commands.py", line 233, in 
run_argv
    return self.run(**all_cmd_args)
  File "C:\Python24\Lib\site-packages\bzrlib\builtins.py", line 386, in run
    br_from = Branch.open(location)
  File "C:\Python24\Lib\site-packages\bzrlib\branch.py", line 118, in open
    t = get_transport(base)
  File "C:\Python24\Lib\site-packages\bzrlib\transport\__init__.py", 
line 361, in get_transport
    return klass(base)
  File "C:\Python24\Lib\site-packages\bzrlib\transport\__init__.py", 
line 376, in _loader
    return klass(base)
  File "C:\Python24\Lib\site-packages\bzrlib\transport\sftp.py", line 
217, in __init__
    self._sftp_connect()
  File "C:\Python24\Lib\site-packages\bzrlib\transport\sftp.py", line 
570, in _sftp_connect
    vendor = _get_ssh_vendor()
  File "C:\Python24\Lib\site-packages\bzrlib\transport\sftp.py", line 
69, in _get_ssh_vendor
    stderr=subprocess.PIPE)
  File "C:\Python24\lib\subprocess.py", line 512, in __init__
    raise ValueError("close_fds is not supported on Windows "
ValueError: close_fds is not supported on Windows platforms