Add active region for operator execution.

This means you can for example, uv unwrap in quad-view and change settings in the toolbar without defaulting back to the first quad-view region available. 

This may be displayed to the user later, for now this is set on executing registrable operators.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54204 954f8c5b-7b00-dc11-b283-0030488c597c