We don't draw the ugly frame for the other panes. So do the same for the mime part tree pane.
We don't draw the ugly frame for the other panes. So do the same for the mime part tree pane.

svn path=/trunk/kdepim/; revision=250620

lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi