CRM-13169 - Corrected file upload issue

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* CRM-13169: Files attached via profile popups don't work
  http://issues.civicrm.org/jira/browse/CRM-13169

Earlier Ajax form submit was not properly used, In pre submit callback of ajaxForm $.ajax(post) was getting called and in it's response it was redirecting to some page, so it was not doing ajax form submit.

I have removed the pre submit callback and added the post submit callback to fix the file upload issue.

I have done the impact analysis and it seems to working fine but I am not very sure why $.ajax is being used in pre submit callback so I am not able analyze the Impact area for that.

please review my patch and let me know if I missed anything in the impact analysis.