CRM-11794 - shorten trigger names and add random string to ensure uniqness

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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 #1793 from dlobo/CRM-11794

CRM-11794 - shorten trigger names and add random string to ensure uniqne...