Merge pull request #741 from AndreMiras/patch-2

tester.Chain.mine() fix

Author: Jan Xie

ethereum/tools/tester.py

@@ -162,7 +162,7 @@ def mine(self, number_of_blocks=1, coinbase=a0):
         assert self.chain.add_block(self.block)
         assert self.head_state.trie.root_hash == self.chain.state.trie.root_hash
         for i in range(1, number_of_blocks):
-            b = make_head_candidate(self.chain, timestamp=self.chain.state.timestamp + 14)
+            b, _ = make_head_candidate(self.chain, timestamp=self.chain.state.timestamp + 14)
             b = Miner(b).mine(rounds=100, start_nonce=0)
             assert self.chain.add_block(b)
         self.block = mk_block_from_prevstate(self.chain, timestamp=self.chain.state.timestamp + 14)