Fix an issue where a documentation symlink can be extracted with an incorrect
owner. This only happens if the distfile is extracted as a non-root user, which
is why nobody has noticed this before (I imagine not many people extract and
build as non-root). Because it's not a big deal and not likely to hit the
majority of users, I'm not bumping PORTREVISION.

Noticed by: Andrzej Tobola (private mail)