CRM-11794 - drop all triggers with civicrm_ prefix

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* CRM-11794: Drop Trigger IF Exists fatals if custom table too long
  http://issues.civicrm.org/jira/browse/CRM-11794
Merge pull request #1797 from dlobo/CRM-11794

CRM-11794 - drop all triggers with civicrm_ prefix