Force the loading of libGpad

git-svn-id: http://root.cern.ch/svn/root/branches/dev/root6-pch@48871 27541ba8-7e3a-0410-8455-c3a389f83636

macros/rootlogon.C

+{
+   gSystem->Load("libGraf.so");
+   gSystem->Load("libGpad.so");
+}