core, core/types: readd transactions after chain re-org

Added a `Difference` method to `types.Transactions` which sets the
receiver to the difference of a to b (NOTE: not a **and** b).

Transaction pool subscribes to RemovedTransactionEvent adding back to
those potential missing from the chain.

When a chain re-org occurs remove any transactions that were removed
from the canonical chain during the re-org as well as the receipts that
were generated in the process.

Closes #1746

core/bench_test.go

@@ -162,7 +162,7 @@ func benchInsertChain(b *testing.B, disk bool, gen func(int, *BlockGen)) {
 
 	// Generate a chain of b.N blocks using the supplied block
 	// generator function.
-	genesis := WriteGenesisBlockForTesting(db, benchRootAddr, benchRootFunds)
+	genesis := WriteGenesisBlockForTesting(db, GenesisAccount{benchRootAddr, benchRootFunds})
 	chain := GenerateChain(genesis, db, b.N, gen)
 
 	// Time the insertion of the new chain.