Copy Python's shutil.copytree into wscript.

It's broken in Python 2.4.4. One gets this message when trying to run
configure:

  [...]
  Checking for SYS_clock_gettime           : ok
  Checking for library rt                  : ok
  Checking for function clock_gettime      : ok
  Checking for function nanosleep          : ok
  Checking for function ceil               : ok
  ---- deps/udns ----
  Traceback (most recent call last):
    File "/path/to/node/tools/waf", line 148, in ?
      Scripting.prepare(t, cwd, VERSION, wafdir)
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Scripting.py", line 102, in prepare
      prepare_impl(t,cwd,ver,wafdir)
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Scripting.py", line 95, in prepare_impl
      main()
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Scripting.py", line 130, in main
      fun(ctx)
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Scripting.py", line 168, in configure
      conf.sub_config([''])
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Configure.py", line 100, in sub_config
      self.recurse(k,name='configure')
    File "/path/to/node/tools/.waf-1.5.8-3e327cd9534c48e6762f56fdb1332663/wafadmin/Utils.py", line 391, in recurse
      f(self)
    File "<string>", line 82, in configure
    File "<string>", line 48, in conf_subproject
    File "/usr/lib/python2.4/shutil.py", line 111, in copytree
      os.mkdir(dst)
  OSError: [Errno 2] No such file or directory: '/sites/rabidlabs.net/sandboxes/m/public_html/projects/0909.node/node/build/default/deps/udns'

The problem is probably this:
http://mail.python.org/pipermail/python-bugs-list/2005-January/027118.html

As a solution I am copying 2.6's version of the function in.