Bug 13582 - Fix redraw region in custom widget.

Cherry-picked from trunk@33870 and reworked for 3.0.x

git-svn-id: svn+ssh://svn.abisource.com/svnroot/abiword/branches/ABI-3-0-0-STABLE@33871 bcba8976-2d24-0410-9c9c-aab3bd5fdfd6