plugin:selection adding new way to force fire 'selectionChange'

[Garry Yao]

There's several use cases around the codebase when interact with CKEDITOR.dom.selection.selectRanges :

1. Just make the selection highlight;
2. Make selection and focus the editor;
3. Only make selection on the fly and fire 'selectionChange' without focus gaining.

For item 1 just invoke the method is ok, for item 2 Martin has already introduce a workarround at ​http://dev.fckeditor.net/ticket/2883#comment:4, for item 3 there's also a workarround by ​http://dev.fckeditor.net/ticket/2862#comment:10.

It's better to integrate these pieces together to avoid confusing.

[Garry Yao]

The problem has expired after recent changesets.