CRM-14513 - fixed the constant being checked - should be CIVICRM_MAIL_LOG.

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* CRM-14513:
  https://issues.civicrm.org/jira/browse/CRM-14513
Merge pull request #3185 from davecivicrm/CRM-14513

CRM-14513 - fixed the constant being checked - should be CIVICRM_MAIL_LO...