Fixed bug where if no-backup option was present, files were never deleted from projects.
Error when a project has no releases (continuation of 9cfd9ca600).
Fix #819. Document how to install for all users on a server.
Fix code comments.
Merge pull request #797 from mortenson/no-backup-remove-files

Fixed bug where if --no-backup was provided, files were never deleted from projects.
Remove pointer to drupal.org/project/drush
Uppercase Drush
When saving root to context system, use realpath()

This resolves the root when you provide a relative path on the CLI like: drush -r ./d7
Fix prior commit. Don't set a value for DRUSH_SELECTED_DRUPAL_ROOT unless you have a root.
Fix #533. Clear cached release XML during 'cc drush' or 'cc all'
Stop using deprecated key_exists().
Fix wrong variable name. Maybe this was subtly breaking some temporary file deletion?
Prevent warning in make when --no-core.