Branches with symlinks can't be exported on Windows

Same complaint (even the same branch!) as #81689, but this bug is for the "export" command, which doesn't yet have the "nice" error message that "branch" does.

56# bzr export ../be
bzr: ERROR: exceptions.AttributeError: 'module' object has no attribute 'symlink'

Traceback (most recent call last):
  File "C:\Python25\Lib\site-packages\bzrlib\commands.py", line 834, in run_bzr_catch_errors
    return run_bzr(argv)
  File "C:\Python25\Lib\site-packages\bzrlib\commands.py", line 790, in run_bzr
    ret = run(*run_argv)
  File "C:\Python25\Lib\site-packages\bzrlib\commands.py", line 492, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "C:\Python25\Lib\site-packages\bzrlib\builtins.py", line 2098, in run
    export(t, dest, format, root)
  File "C:\Python25\Lib\site-packages\bzrlib\export\__init__.py", line 97, in export
    return _exporters[format](tree, dest, root)
  File "C:\Python25\Lib\site-packages\bzrlib\export\__init__.py", line 61, in _loader
    return func(tree, dest, root)
  File "C:\Python25\Lib\site-packages\bzrlib\export\dir_exporter.py", line 47, in dir_exporter
    ie.put_on_disk(dest, dp, tree)
  File "C:\Python25\Lib\site-packages\bzrlib\inventory.py", line 342, in put_on_disk
    self._put_on_disk(fullpath, tree)
  File "C:\Python25\Lib\site-packages\bzrlib\inventory.py", line 769, in _put_on_disk
    os.symlink(self.symlink_target, fullpath)
AttributeError: 'module' object has no attribute 'symlink'

bzr 1.2.0 on python 2.5.1.final.0 (win32)
arguments: ['C:\\Python25\\Scripts\\bzr', 'export', '../be']
encoding: 'cp1252', fsenc: 'mbcs', lang: None
plugins:
  difftools C:\Users\Adrian\AppData\Roaming\bazaar\2.0\plugins\difftools [0.91.0]
  gtk C:\Users\Adrian\AppData\Roaming\bazaar\2.0\plugins\gtk [0.94.0dev0]
  launchpad C:\Python25\lib\site-packages\bzrlib\plugins\launchpad [unknown]
  multiparent C:\Python25\lib\site-packages\bzrlib\plugins\multiparent.py [unknown]
  svn C:\Users\Adrian\AppData\Roaming\bazaar\2.0\plugins\svn [0.4.7]
  xml C:\Users\Adrian\AppData\Roaming\bazaar\2.0\plugins\xml [0.4.1]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.