Added cache_valid_time option to apt module
Updated apt module documentation string with a cache_valid_time explanation
Updated cache_valid_time option to check the update timestamp if update-notifier-common is installed.
mtime of the apt lists is used as fallback.
apt module cache_valid_time documentation fix
Merge branch 'devel_apt-cache_valid_time' of git://github.com/gottwald/ansible into devel