Only throw error when employers are involved.
-- CRM-13400, removed obsolete code and fixed default settting of current membership

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* CRM-13400: Online membership renewal via contribution page no longer sets existing membership as default
  http://issues.civicrm.org/jira/browse/CRM-13400
--CRM-12970, fixed for more then one discount set

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* CRM-12970: civicrm_price_field_value not removed for discount price set
  http://issues.civicrm.org/jira/browse/CRM-12970
Merge pull request #1555 from donordepot/master

Only throw error when employers are involved.
Merge pull request #1683 from pradpnayak/CRM-12970

--CRM-12970, fixed for more then one discount set
Merge pull request #1682 from pradpnayak/CRM-13400

-- CRM-13400, removed obsolete code and fixed default settting of curren...