this makes the database package entry smaller, and we propbably
get more fields to installed_package later too. this cleans up
the way scripts are stored and is a preparation for supporting
triggers. some parsing for trigger meta-data. ref #45.

so user can override trusted keys directory and repositories file.

they are not needed, and cause errors if signing keys are not
present.

usually we are interested on the actual file's length. but
audit is interested about the link. so add a flag for this and
use it in audit.

make the system audit compare only installed files, instead of
scanning the whole file system. also make it print only package
names with -q, so reinstalling modified packages becomes easy.

this way we never change cwd, and relative filenames are always
parsed consistently. this also helps filename construction in many
places. this patch also changes '--root' to override location of
all configuration to be in the new root. previously it depended
on the file which one was used.

also take precautions in audit code if the db is missing the
checksum.

and use it for /etc/init.d by default. fixes #99.

to check system files for changes.