SYTLE: cache pointer to dataset
SYTLE: cache pointer to dataset

The getDataset() function appear to have some extra overhead, so
try caching and reusing the pointer.  Didn't do timing tests, but
the performance seems the same or better than before.

pieper/CTK,ddao/CTK,SINTEFMedtek/CTK,fedorov/CTK,151706061/CTK,laurennlam/CTK,espakm/CTK,CJGoch/CTK,151706061/CTK,SINTEFMedtek/CTK,151706061/CTK,AndreasFetzer/CTK,fedorov/CTK,vovythevov/CTK,mehrtash/CTK,commontk/CTK,danielknorr/CTK,CJGoch/CTK,pieper/CTK,lassoan/CTK,msmolens/CTK,ddao/CTK,mehrtash/CTK,AndreasFetzer/CTK,laurennlam/CTK,espakm/CTK,lassoan/CTK,rkhlebnikov/CTK,msmolens/CTK,msmolens/CTK,sankhesh/CTK,SINTEFMedtek/CTK,danielknorr/CTK,rkhlebnikov/CTK,msmolens/CTK,commontk/CTK,naucoin/CTK,lassoan/CTK,ddao/CTK,sankhesh/CTK,AndreasFetzer/CTK,vovythevov/CTK,commontk/CTK,finetjul/CTK,finetjul/CTK,rkhlebnikov/CTK,CJGoch/CTK,151706061/CTK,Heather/CTK,jcfr/CTK,sankhesh/CTK,fedorov/CTK,Sardge/CTK,laurennlam/CTK,sankhesh/CTK,espakm/CTK,SINTEFMedtek/CTK,CJGoch/CTK,AndreasFetzer/CTK,Heather/CTK,jcfr/CTK,Heather/CTK,pieper/CTK,mehrtash/CTK,ddao/CTK,danielknorr/CTK,jcfr/CTK,naucoin/CTK,rkhlebnikov/CTK,vovythevov/CTK,jcfr/CTK,Heather/CTK,laurennlam/CTK,fedorov/CTK,SINTEFMedtek/CTK,danielknorr/CTK,naucoin/CTK,pieper/CTK,Sardge/CTK,lassoan/CTK,naucoin/CTK,espakm/CTK,CJGoch/CTK,vovythevov/CTK,finetjul/CTK,Sardge/CTK,finetjul/CTK,jcfr/CTK,commontk/CTK,Sardge/CTK,mehrtash/CTK,151706061/CTK