Fixed issue 06171: variable < X is true even if variable isn't answered
Dev This now works automatically for authors who use the conditions editor
Dev To bulk-convert the entire database, call http://localhost/limesurvey/admin/admin.php?action=EMtest&subaction=upgrade_conditions2relevance
Dev Authors who manually enter relevance equations must pay more attention to the upgrade hints - http://docs.limesurvey.org/Upgrade+hints+for+version+1.92#Mathematical_comparisons_against_empty_no_responses