Be stricter in processing unrequested blocks

AcceptBlock will no longer process an unrequested block, unless it has not
been previously processed and has more work than chainActive.Tip()

src/test/miner_tests.cpp

@@ -84,7 +84,7 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
         pblock->hashMerkleRoot = pblock->BuildMerkleTree();
         pblock->nNonce = blockinfo[i].nonce;
         CValidationState state;
-        BOOST_CHECK(ProcessNewBlock(state, NULL, pblock));
+        BOOST_CHECK(ProcessNewBlock(state, NULL, pblock, true, NULL));
         BOOST_CHECK(state.IsValid());
         pblock->hashPrevBlock = pblock->GetHash();
     }