docker-buildpackage - easily build deb/apt packages

Prerequisites:

automatically debootstrap a build container base image
build deb's by launching a container, running the build inside it, pull out the deb's and cleanup again

call dck-buildpackage --target <target_name>
creates an installable apt repo (needs an gpg key)
gpg key id can be set via $DCK_BUILDPACKAGE_SIGNKEY (otherwise use default)
if distro config sets $DISTRO_APT_USE_BUILT_REPO=1, the repo will automatically be added to the build containers

Variable	Description
`$DCK_BUILDPACKAGE_SIGNKEY`	ID of the GPG key to be used for repo signing (if absent, use GPGs default sign key)
`$DCK_BUILDPACKAGE_TARGET_REPO`	prefix of the generated apt repos. each target has its own repo in subdir named by target.
`$DCK_BUILDPACKAGE_CONFDIR`	config directory (defaults ./cf relative to the dck-buildpackage main script)
`$DCK_BUILDPACKAGE_TARBALL_CACHE`	cache dir for chroot tarballs (if set, don't remove tarballs and reused for image import)
`$DISTRO_TARGET_REPO`	actual target repo directory, derived from `$DCK_BUILDPACKAGE_TARGET_REPO` if not given.

publishing built packages to remote repos
a decent manpage :o
installable package of this tool
cloning git repos instead of using local source tree
should dck-buildpackage --cleanup also remove base images ?
support subdirs and dots in target names (docker names/tags are derived from that, and it doesn't like some chars in there)
add finer per-target configuration of base image, volume, container names
add cleanup for only one specific target
per package cache images, so deps need to be deployed only once
separate clean for only apt-cache, base images, containers, ...
command line option for separate configs
honor .gitignore in source trees (dont upload ignored files)