center the zooming on the middle point between the two fingers when doing pinch zoom
center the zooming on the middle point between the two fingers when doing pinch zoom

svn path=/trunk/KDE/kdeedu/marble/; revision=1071413

probonopd/marble,David-Gil/marble-dev,oberluz/marble,tucnak/marble,probonopd/marble,Earthwings/marble,David-Gil/marble-dev,rku/marble,quannt24/marble,tucnak/marble,oberluz/marble,utkuaydin/marble,tzapzoor/marble,tucnak/marble,quannt24/marble,tucnak/marble,tzapzoor/marble,adraghici/marble,oberluz/marble,Earthwings/marble,David-Gil/marble-dev,probonopd/marble,AndreiDuma/marble,utkuaydin/marble,Earthwings/marble,tucnak/marble,utkuaydin/marble,tucnak/marble,probonopd/marble,oberluz/marble,rku/marble,adraghici/marble,David-Gil/marble-dev,Earthwings/marble,David-Gil/marble-dev,probonopd/marble,tzapzoor/marble,tzapzoor/marble,adraghici/marble,utkuaydin/marble,rku/marble,quannt24/marble,utkuaydin/marble,rku/marble,probonopd/marble,tzapzoor/marble,AndreiDuma/marble,AndreiDuma/marble,tzapzoor/marble,AndreiDuma/marble,quannt24/marble,oberluz/marble,quannt24/marble,rku/marble,AndreiDuma/marble,rku/marble,probonopd/marble,David-Gil/marble-dev,tucnak/marble,adraghici/marble,quannt24/marble,AndreiDuma/marble,oberluz/marble,tzapzoor/marble,utkuaydin/marble,Earthwings/marble,Earthwings/marble,quannt24/marble,adraghici/marble,adraghici/marble,tzapzoor/marble