CRM-15030, fixed the display of custom data of type checkbox in views

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* CRM-15030: Custom fields in Views display incorrectly or not at all, depending on label
  https://issues.civicrm.org/jira/browse/CRM-15030
Merge pull request #154 from kurund/CRM-15030

CRM-15030, fixed the display of custom data of type checkbox in views