add unselectable IE attribute to wymiframe to prevent IE from losing
cursor focus when inserting plugin object (thus throwing escaped HTML to
the top of the area).

Tested in FF18, Chrome 23, Safari 5.1.7 (win), IE8, IE9, IE10.
Merge pull request #1582 from at3560k/develop

Add unselectable IE attribute to wymiframe to prevent IE from losing focus