CRM-13904 - Improve proximity query accuracy

http://issues.civicrm.org/jira/browse/CRM-13904
CRM-13904 - add links to formula used

----------------------------------------
* CRM-13904: Improve proximity query accuracy
  http://issues.civicrm.org/jira/browse/CRM-13904
Merge pull request #2153 from dlobo/CRM-13904

CRM-13904 - Improve proximity query accuracy