CRM-13449 : while onclick on submit button - putting execution of disbled = true inside timeout function to process the submit of form and then disbling submit button

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* CRM-13449: send email activity: submit button in Chrome
  http://issues.civicrm.org/jira/browse/CRM-13449
Merge pull request #1700 from pratik-joshi/CRM-13449

CRM-13449 : while onclick on submit button - putting execution of disbled = true inside timeout function to process the submit of form and then disbling submit button