BR tags replaced with NBSPs

[Jeremy Jannotta]

In all versions of CKEditor version 4.x, we've noticed that BR tags are automatically replaced with   entities at the top level. If you try to add them back in with the ENTER key via wysiwyg, or source, they are replaced.

We think this is unintuitive, possibly a bug, and at the very least should have an option to turn off this behavior, as it is preventing our upgrade from 3.x to 4.

Test case: ​http://jsfiddle.net/jpj109/97XeC/

Steps to reproduce:

1. Paste or type HTML into the source field that contains one or more BR tags at the top level (not enclosed within another tag)
2. Toggle back to WYSIWYG field
3. Toggle back to source field
4. Notice where the BR tags are now a  

Expected results: Any BR tags originally entered into source should remain

[Jakub Ś]

This is in fact dup of #10146.