Fix categorised renderer does not store changes to the source symbol

Avoids the frustrating situation where changes to a symbol in the
categorised renderer are lost when the layer properties window
is reopened

Also fix a leak in the Python bindings

(cherry-picked from 3744ac2)

python/core/symbology-ng/qgsgraduatedsymbolrendererv2.sip

@@ -210,7 +210,7 @@ class QgsGraduatedSymbolRendererV2 : QgsFeatureRendererV2
     void updateColorRamp( QgsVectorColorRampV2* ramp /Transfer/ = 0, bool inverted = false );
 
     /** Update all the symbols but leave breaks and colors. */
-    void updateSymbols( QgsSymbolV2* sym /Transfer/ );
+    void updateSymbols( QgsSymbolV2* sym );
 
     void setRotationField( QString fieldOrExpression );
     QString rotationField() const;

src/core/symbology-ng/qgscategorizedsymbolrendererv2.cpp

@@ -763,6 +763,7 @@ void QgsCategorizedSymbolRendererV2::updateSymbols( QgsSymbolV2 * sym )
     updateCategorySymbol( i, symbol );
     ++i;
   }
+  setSourceSymbol( sym->clone() );
 }
 
 void QgsCategorizedSymbolRendererV2::setScaleMethod( QgsSymbolV2::ScaleMethod scaleMethod )

src/gui/symbology-ng/qgscategorizedsymbolrendererv2widget.cpp

@@ -536,7 +536,7 @@ void QgsCategorizedSymbolRendererV2Widget::changeCategorizedSymbol()
   QgsSymbolV2* newSymbol = mCategorizedSymbol->clone();
 
   QgsSymbolV2SelectorDialog dlg( newSymbol, mStyle, mLayer, this );
-  if ( !dlg.exec() )
+  if ( !dlg.exec() || !newSymbol )
   {
     delete newSymbol;
     return;