When encoding to CNF via ABC, use the simple mapping if there are more than 10M nodes. This is because currently ABC seems to have a 4GB memory limit internally. So any more than about 10M nodes maxes out the memory.
When encoding to CNF via ABC, use the simple mapping if there are more than 10M nodes. This is because currently ABC seems to have a 4GB memory limit internally. So any more than about 10M nodes maxes out the memory.

git-svn-id: 5069ba8be4c997ee907bf46f8ec9a2bbfb655637@1016 e59a4935-1847-0410-ae03-e826735625c1

linpc/STP,linpc/STP,linpc/STP,linpc/STP,linpc/STP