as discussed in http://lists.alpinelinux.org/alpine-devel/3122.html

introduce post_unpack that by default will search for config.sub and
config.guess and replace those if found.

we ship our own version of those files

check for pkguser, pkggroup, subpackage

seems like it moved in recent busybox. we need to support both variants

some apkbuilds use it in global context

- we need check arch for noarch
- we need list packages generated from $linguas

so subfunctions don't overwrite the global variables like depends, pkgdesc etc.

via ABUILD_LOG_CMD config option

This is supposed to be used on the build servers

fixes regression

so we dont leak functions like 'build' and other variables.

syslinux switched to elf format from 5.0

This is an alternative to saveas-*:// which should be slightly more
intuitive. It also is similar to what arch linux does.

This has the nice effect that we get the index automatically built for
our REPODEST.

Discussion here:
http://lists.alpinelinux.org/alpine-devel/0249.html

fixes #1477