CRM-13572 - Upgrader - Display pre-upgrade message about OFC

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* CRM-13572:
  http://issues.civicrm.org/jira/browse/CRM-13572
CRM-13572 - Upgrader - Delete OFC file and/or display message

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* CRM-13572:
  http://issues.civicrm.org/jira/browse/CRM-13572
Merge pull request #1788 from totten/4.3-ofc-delete

CRM-13572 - Upgrader - Delete OFC file and/or display message