mingw: keep trailing slashes for _wchdir() and readlink()

This is needed so that `_wchdir()` can be used with drive root
directories, e.g. C:\ (`_wchdir("C:")` fails to switch the directory
to the root directory).

This fixes msysgit#359 (in Git for Windows
2.x only, though).

Likewise, `readlink()`'s semantics require a trailing slash for symbolic
links pointing to directories. Otherwise all checked out symbolic links
pointing to directories would be marked as modified even directly after a
fresh clone.

This fixes git-for-windows#210

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -375,9 +375,6 @@ static wchar_t *normalize_ntpath(wchar_t *wbuf)
 	for (i = 0; wbuf[i]; i++)
 		if (wbuf[i] == '\\')
 			wbuf[i] = '/';
-	/* remove potential trailing slashes */
-	while (i && wbuf[i - 1] == '/')
-		wbuf[--i] = 0;
 	return wbuf;
 }