Support for multi-select in the conversation list.

Unfortunately I'm pretty sure this is the only way to do multi-select on both <> Honeycomb. It'd be nice if we could use the new stuff they were experimenting with in #1601, but I don't think it'll be backwards compatible.
and here sth. like this:

```JAVA

    setActionTitle(messageRecords.size());
  }

  private void setActionTitle(Integer count)
  {
    if (actionMode == null) return;

    if (count > 1) {
      actionMode.setTitle(R.string.conversation_fragment_cab__batch_selection_mode);
      actionMode.setSubtitle(getString(R.string.conversation_fragment_cab__batch_selection_amount, count));
    }
    else {
      actionMode.setTitle("");
      actionMode.setSubtitle("");
    }
  }
```

tested on GB