Can't submit "Actions" on list form

Hey,

Found a little bug in the javascript file: privatemsg-list.js

The current code is as follows:

$('#privatemsg-list #edit-operation').change(function () {
  $('#edit-submit').click();
});

The "#edit-submit" id is not reliable because other forms on the page may cause it to be incremented ("edit-submit-2", etc.)

I have attached a patch that fixes this by making the following change:

$('#privatemsg-list #edit-operation').change(function () {
  $('div.privatemsg-op-button input.form-submit').click();
});

Cheers!