Skip writable_dir test on Windows

It doesn't seem possible to create a dir that the owner can't write to
on Windows, so the test doesn't run properly.  If the test can be
updated to reliably create/find a user read-only directory (probably via
NTFS ACLs and win32security), then it can be unskipped.

IPython/utils/tests/test_path.py

@@ -381,6 +381,7 b' def test_get_long_path_name():'
     p = path.get_long_path_name('/usr/local')
     nt.assert_equals(p,'/usr/local')
 
[e-mail]_win32 # can't create not-user-writable dir on win
 @with_environment
 def test_not_writable_ipdir():
     tmpdir = tempfile.mkdtemp()