[PLG_CRON_SUPPORT] Try to prevent mailing same user more than once
[PLG_CRON_SUPPORT] Try to prevent mailing same user more than once

anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms,zweidner/hubzero-cms,zweidner/hubzero-cms,zooley/hubzero-cms,zooley/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms