bug #728 convert encryption protocol value to lower case (serieznyi)

This PR was squashed before being merged into the 5.x branch (closes #728).

Discussion
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convert encryption protocol value to lower case

I spent the whole day could not understand why I am unable to send mail and I get the next error
`Connection could not be established with host smtp.yandex.ru [Unable to find the socket transport "SSL" - did you forget to enable it when you configured PHP? #1]`
I soon realized that the Protocol specify the encryption systems in the upper register. I was very pleasantly surprised that no one has foreseen such a possibility. So I decided to fix it

Commits
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483f1fc convert encryption protocol value to lower case

lib/classes/Swift/Transport/EsmtpTransport.php

@@ -140,6 +140,10 @@ public function getTimeout()
      */
     public function setEncryption($encryption)
     {
+        if (is_string($encryption)) {
+            $encryption = strtolower($encryption);    
+        }
+
         if ('tls' == $encryption) {
             $this->_params['protocol'] = 'tcp';
             $this->_params['tls'] = true;