CRM-14971 - Contact image URLs should go through WP frontend

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* CRM-14971: Contact image URLs broken in WordPress after upgrade to 4.4.6
  https://issues.civicrm.org/jira/browse/CRM-14971
CRM-14971 - CRM_Upgrade - Change backend image_URLs to frontend image_URLs

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* CRM-14971: Contact image URLs broken in WordPress after upgrade to 4.4.6
  https://issues.civicrm.org/jira/browse/CRM-14971
Merge pull request #3647 from totten/4.4-wp-images

CRM-14971 - Contact image URLs should go through WP frontend