CRM-12940, towards allowing extension to alter core search

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* CRM-12940: Allow extensions to participate in CRM_*_BAO_Query
  http://issues.civicrm.org/jira/browse/CRM-12940
CRM-12940, extending core search via hook_civicrm_queryObjects

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* CRM-12940: Allow extensions to participate in CRM_*_BAO_Query
  http://issues.civicrm.org/jira/browse/CRM-12940
CRM-12940

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* CRM-12940: Allow extensions to participate in CRM_*_BAO_Query
  http://issues.civicrm.org/jira/browse/CRM-12940
Merge pull request #1162 from deepak-srivastava/search

CRM-12940