Disallow parent dir components (..) in open_basedir() at runtime

[iluuu1994]

Fix GH-10469

[bukka]

@iluuu1994 Did you just prohibit .. anywhere in the path? If so, it should be changed to not allow only jump out of cwd (you can count the dirs...)

[iluuu1994]

@bukka Oh, that's a good idea. I missed this approach. I'll make the changes tomorrow. I suppose then backporting it would be fine too.