L::Path: Precompute "sorted children"

It saves ~0.2 seconds when processing Lintian.

Signed-off-by: Niels Thykier <niels@thykier.net>
L::Util: Cache the UTF-8 decoder

Signed-off-by: Niels Thykier <niels@thykier.net>
L::Check: Inline a qr//-result that is only used once

Signed-off-by: Niels Thykier <niels@thykier.net>
d/changelog: Open entry for 2.5.29

Signed-off-by: Niels Thykier <niels@thykier.net>