Bring back "KLinkItemSelectionModel: Synchronize currentIndex"

The changes from this commit were initially committed to KDE/4.11
as 14e2ff5b, but I asked for it to
be reverted before 4.11.1 went out because it caused a bad regression
in Gwenview. It was thus reverted by commit 26201fd9.

The fix for the regression in Gwenview has just been committed, so
I am bringing back this one.

CCMAIL:release-team@kde.org