correction from Scrawl.

Now correctly handles skills/attributes.
Also, document what ContentSelectorView::ContentSelector::slotAddonTableItemActivated() is doing.

apps/openmw/mwmechanics/activespells.cpp

@@ -185,7 +185,7 @@ namespace MWMechanics
             bool missing = true;
             for (std::vector<ActiveEffect>::const_iterator iter(addTo.begin()); iter != addTo.end(); ++iter)
             {
-                if (effect->mEffectId == iter->mEffectId)
+                if ((effect->mEffectId == iter->mEffectId) && (effect->mArg == iter->mArg))
                 {
                     missing = false;
                     break;

components/contentselector/view/contentselector.cpp

@@ -183,6 +183,7 @@ void ContentSelectorView::ContentSelector::setGameFileSelected(int index, bool s
 
 void ContentSelectorView::ContentSelector::slotAddonTableItemActivated(const QModelIndex &index)
 {
+    // toggles check state when an AddOn file is double clicked or activated by keyboard
     QModelIndex sourceIndex = mAddonProxyModel->mapToSource (index);
 
     if (!mContentModel->isEnabled (sourceIndex))