CRM-12880 and CRM-11784 help text improvements.

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* CRM-12880: ACL help text could be slightly clearer?
  http://issues.civicrm.org/jira/browse/CRM-12880
* CRM-11784: user text for civicrm/event/manage
  http://issues.civicrm.org/jira/browse/CRM-11784
Merge pull request #1047 from davecivicrm/CRM-12880

CRM-12880 and CRM-11784 help text improvements.