- rmdir / unlink no longer follow the final symlink
 - rmdir / unlink no longer check write permission on the found object, but on its parent
 - rmdir should return EBUSY when path matches the root / cwd
 - unlinking a directory should return EPERM according to POSIX (EISDIR is a Linux convention)
Merge pull request #1388 from inolen/unlink_fixes

misc unlink / rmdir fixes