Double printing fix

Fix double printing problem within the MailerMailer Settings page in the admin panel. The problem was due to the way wordpress registers variables. When registering new variables wordpress makes a call to add (to first add the variable to the db) then update (which updates the value). Both add and update make calls to the same function used to sanitize user input causing the notification to appear twice. More on this issue can be found here http://codex.wordpress.org/Function_Reference/register_setting#Notes

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