Log Message:
Update to 2.5.0beta2:

* The feature to confirm missing attachments was added.
* The feature to confirm recipients before sending was added.
* To: header is also searched by quick search in Sent/Draft/Queue folders.
* 'Edit/Quick search' menu was added.
* Spaces in address and server entries on account preferences dialog
  are now automatically removed when applied.
* The address completion was fixed.
* The compilation failure with GTK+ <= 2.8 was fixed.
* Win32: --attach option was fixed.