Improve selection behaviour concerning the new "jump to next/previous

Improve selection behaviour concerning the new "jump to next/previous
row using right/left arrow" and "jump to next/previous column using
down/up arrow" when using the Icon View's "Rows" and "Columns"
arrangement, respectively, in the following cases:

1. In "Columns" arrangement, if the first item is selected and
Ctrl-Down is pressed repeatedly, don't deselect the first item when
jumping to the next column.

2. In "Rows" arrangement, if the first item in the second row is
active and then Left and finally Shift-Left is pressed, don't
re-select the first item in the second row unexpectedly.

3. If an item in the middle of the second row is selected, make sure
that selection with Shift-Left/Shift-Right is reversible even if the
previous/next row is reached.

svn path=/trunk/KDE/kdebase/apps/; revision=996758