CRM-13075 - CRM_Core_BAO_Block - Allow handlePrimary() with entities from extensions

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* CRM-13075: Mark is_primary for HRJob records
  http://issues.civicrm.org/jira/browse/CRM-13075
Merge pull request #1295 from totten/master-isprimary-tables

CRM-13075 - CRM_Core_BAO_Block - Allow handlePrimary() with entities from extensions