CRM-13377 - Manipulate the main "Send Email" button but not the "Cancel" button

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* CRM-13377: "Send email" produces double "Processing" button
  http://issues.civicrm.org/jira/browse/CRM-13377
Merge pull request #1629 from totten/master-email-proc-btn

CRM-13377 - Manipulate the main "Send Email" button but not the "Cancel"...