Don't include system.module for versions > 6.x
Complete pm_update_filter() docs with all possible update status.
Fix update_info engine for Drupal 8.
Fix case statement in pm_update_filter().
Fix typo.
Remove lock/unlock capability from pm-updatestatus command.
Revert "Remove lock/unlock capability from pm-updatestatus command."

This reverts commit fbc827eecb79d857a672520a05c093e1c6e6370b.
Fix doxygen in cache related code.
Remvoe unused and undocumented $headers parameter in \Drush\Cache\FileCache::set()
Restore 'Update information last refreshed...' mesage.
Check cache file exists before trying to delete it.
Fix #839. Use DRUSH_DRUPAL_CORE when building a require statement.