Fix email address comparison issue

When comparing the From address of incoming email. If the ticket owner sent
an email back into the system and the email address did not match exactly,
case-wise, the email would not be considered from the ticket owner.

include/class.thread.php

@@ -533,7 +533,7 @@ function postEmail($mailinfo) {
         // Disambiguate if the user happens also to be a staff member of the
         // system. The current ticket owner should _always_ post messages
         // instead of notes or responses
-        if ($mailinfo['email'] == $ticket->getEmail()) {
+        if (strcasecmp($mailinfo['email'], $ticket->getEmail()) == 0) {
             $vars['message'] = $body;
             return $ticket->postMessage($vars, 'Email');
         }