fix deprecation warnings introduced by API changes in libarchive3

in addition clean up the LibArchive cmake description as it is included in
cmake 2.8.8 or later

Signed-off-by: Matthias Maennich <matthias@maennich.net>
determine shell with $BASH and $ZSH_NAME

this is more reliable (especially in subshells)
see http://www.stackoverflow.com/a/3327022 for details

Reported-by: Det
Signed-off-by: Matthias Maennich <matthias@maennich.net>