Problem when changing the queue while emerging

[René 'Necoro' Neumann]

The queue should not be changed, while emerge is working at it. Doing it nevertheless, yields errors like:

Traceback (most recent call last):
  File "/usr/lib64/python2.6/site-packages/portato/gui/windows/main.py", line 1841, in cb_package_emerge_clicked
    return self.packageTable.cb_package_emerge_clicked(*args)
  File "/usr/lib64/python2.6/site-packages/portato/gui/windows/main.py", line 309, in cb_package_emerge_clicked
    self._update_keywords(True)
  File "/usr/lib64/python2.6/site-packages/portato/gui/windows/main.py", line 201, in _update_keywords
    self.queue.append(self.pkg.get_cpv(), type = type, update = update)
  File "/usr/lib64/python2.6/site-packages/portato/gui/queue.py", line 279, in append
    for c in self.iters[type]:
RuntimeError: dictionary changed size during iteration

To fix it:

First step: Check that the queue cannot be changed.
Second step: Allow multiple queues.