Add ability to disable content-disposition for email attachments.

This solves issues with outlook and text/calendar attachments.

Refs #3042

lib/Cake/Network/Email/CakeEmail.php

@@ -1355,7 +1355,9 @@ protected function _attachFiles($boundary = null) {
 			$msg[] = '--' . $boundary;
 			$msg[] = 'Content-Type: ' . $fileInfo['mimetype'];
 			$msg[] = 'Content-Transfer-Encoding: base64';
-			$msg[] = 'Content-Disposition: attachment; filename="' . $filename . '"';
+			if (!isset($fileInfo['contentDisposition']) || $fileInfo['contentDisposition']) {
+				$msg[] = 'Content-Disposition: attachment; filename="' . $filename . '"';
+			}
 			$msg[] = '';
 			$msg[] = $data;
 			$msg[] = '';