win32: bzr can't set file attribute to hidden if file path contains unicode.

[methane]

bzr uses "win32file.SetFileAttributes" to set file attribute.
But bzr should use "win32file.SetFileAttributesW" for path contains charactor not in current codepage.

In bzrlib/win32util.py:

 def set_file_attr_hidden(path):
     """Set file attributes to hidden if possible"""
     if has_win32file:
- win32file.SetFileAttributes(path, win32file.FILE_ATTRIBUTE_HIDDEN)
+ win32file.SetFileAttributesW(path, win32file.FILE_ATTRIBUTE_HIDDEN)

(Relating to: http://bugs.launchpad.net/tortoisebzr/+bug/335362/comments/41)