implement SH_ItemView_ActivateItemOnSingleClick in kde4

Was in Plasma/5.3, but that branch didn't get merged into master
Now it's too diverged to try

kstyle/kstylekde4compat.cpp

@@ -34,6 +34,11 @@ KStyleKDE4Compat::~KStyleKDE4Compat()
 int KStyleKDE4Compat::styleHint(StyleHint hint, const QStyleOption *option, const QWidget *widget, QStyleHintReturn *returnData) const
 {
     switch (hint) {
+    case SH_ItemView_ActivateItemOnSingleClick: {
+        KConfigGroup g(KSharedConfig::openConfig(), "KDE");
+        return g.readEntry("SingleClick", true);
+    }
+
     case SH_DialogButtonBox_ButtonsHaveIcons: {
         // was KGlobalSettings::showIconsOnPushButtons() :
         KConfigGroup g(KSharedConfig::openConfig(), "KDE");