mini sudo that checks if user is in "abuild" group and allows it to
run apk, adduser adn addgroup as root

ref #951

fixes #955

For a second, indented message line.

We need locking Since the build servers use a shared download dir
and multiple vservers might want download same file at same time.

fixes #873

So we can set pkgname if it differs from download archive name

curl does not fail by default. it downloads the 404 error page instead
so we need add -f option to curl.

Not been used for ages.

fixes #871

This is to avoid things like:
http://git.alpinelinux.org/cgit/aports/commit/?id=81c0a4bb37e709ebc5add8394331d28209a61b6f

apk takes files that starts with - as params.

build-list will list which aports that has missing packages

rebuild-list will list which aports that has outdated packages, i.e. when
APKBUILD is newer than the apk