#52: Automatically set the label separator to the list separator when csv, etc. is selected with @sites (or other multi-site commands)
#52: Simplify code to automatically set the label separator.
Add suggestions from #56.
drush_valid_drupal_root() requires only a file called includes/common.inc to match a Drupal directory, which causes problems when this file pattern appears elsewhere, in non-Drupal root contexts (e.g. in module_builder module).
Refactor drush_valid_drupal_root() to avoid a second function with checks.