added Fokker-Planck finite difference operator for BS, square root and Heston processes

git-svn-id: https://quantlib.svn.sourceforge.net/svnroot/quantlib/trunk/QuantLib@18437 8618b1d8-e22c-0410-b026-96a5dba3e089
updated vc10 project file

git-svn-id: https://quantlib.svn.sourceforge.net/svnroot/quantlib/trunk/QuantLib@18438 8618b1d8-e22c-0410-b026-96a5dba3e089