Add rcube_message_header class (alias for rcube_mail_header) definition to prevent

errors when trying to use cached message objects created in master (0.9) version

program/include/rcube_imap_generic.php

@@ -60,7 +60,7 @@ class rcube_mail_header
     public $others = array();
     public $flags = array();
 
-    // map header to rcube_message_header object property
+    // map header to rcube_mail_header object property
     private $obj_headers = array(
         'date'      => 'date',
         'from'      => 'from',
@@ -118,6 +118,11 @@ class iilBasicHeader extends rcube_mail_header
 {
 }
 
+// Support objects created in git-master (0.9)
+class rcube_message_header extends rcube_mail_header
+{
+}
+
 /**
  * PHP based wrapper class to connect to an IMAP server
  *