antimake: follow symlinks when searching extensions
socket: getpeercreds() - getpeereid() + pid

Most OSes have also way to get pid of unix socket peer.

Provide generic API for fetching it.

Make compat getpeereid() wrap it, so all compat goo
is in one place.
cfparser: require that first section must be present

otherwise, when run on empty file, the main section defaults
are not filled in and program may crash.