use caching of vertex matches to speed up the VF2 searches

git-svn-id: svn://svn.code.sf.net/p/rdkit/code/trunk@2462 a5045d30-4826-4484-9c7f-6e55a06ddc77
set props

git-svn-id: svn://svn.code.sf.net/p/rdkit/code/trunk@2463 a5045d30-4826-4484-9c7f-6e55a06ddc77