Changes cursor when mouse enters ctkSearchBox

clear button.

See http://na-mic.org/Mantis/view.php?id=1347

I don't really like the choice of cursor, but didn't find another good one. At the same time, I don't know that an eraser bitmap is applicable here either. Here is a good list of cursor shapes: http://qt-project.org/doc/qt-4.8/qt.html#CursorShape-enum