anna uses a retriever to download udebs, checks their consistency, and
calls udpkg to install them. It can be called as follows:

anna <retriever>

	Use the given retriever, get the list of all udebs it can
	retrieve, work out which to install by default, prompt the user 
	for which to install, and install all selected.

anna <retriever> default

	Same as above, except that the retriever is stored as the default
	retriever to use.

anna install <udeb ..>

	Uses the default retriever to get the specified udebs and installs
	them. Dependencies will automatically be installed too. Note that
	this still needs a debconf frontend to be running, so use of the
	anna-install command in debian-installer-utils is better for
	command-line use.