CRM-14789 - Translate and tweak the error message when attempting to delete case type which is in use.

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* CRM-14789:
  https://issues.civicrm.org/jira/browse/CRM-14789
Merge pull request #3661 from davecivicrm/CRM-14789

CRM-14789 - Translate and tweak the error message when attempting to del...