Add "lstat" replacement to "ghar_win"

The ghar main module uses "os.lstat()" to figure out whether a directory
entry is a directory, file or symlink. Implement a ghar-specific
substitute for "lstat" that can detect symlinks.
Clean up code "ghar_win.py"
Fix handling of symlinked directories on Windows

Add various tweaks to ensure proper handling of symlinked directories on
Windows.
Move 'symlinked folder unlink' fix into 'ghar_win'

Let the "ghar_win" module monkeypatch the "os.unlink" function, so that
"ghar" can just use its original code for removing symlinked folders;
the new "os.unlink" version installed by "ghar_win" can then decide to
call the right function on Windows.