Avoid unnecessary temp block and copy ctor

block already has a default ctor, and the extra object
churn due to its innards (vectors, etc) is pointless.

src/cryptonote_basic/miner.cpp

@@ -146,7 +146,7 @@ namespace cryptonote
   //-----------------------------------------------------------------------------------------------------
   bool miner::request_block_template()
   {
-    block bl = AUTO_VAL_INIT(bl);
+    block bl;
     difficulty_type di = AUTO_VAL_INIT(di);
     uint64_t height = AUTO_VAL_INIT(height);
     uint64_t expected_reward; //only used for RPC calls - could possibly be useful here too?

src/cryptonote_core/blockchain.cpp

@@ -404,7 +404,7 @@ bool Blockchain::init(BlockchainDB* db, const network_type nettype, bool offline
   if(!m_db->height())
   {
     MINFO("Blockchain not loaded, generating genesis block.");
-    block bl = boost::value_initialized<block>();
+    block bl;
     block_verification_context bvc = boost::value_initialized<block_verification_context>();
     generate_genesis_block(bl, get_config(m_nettype).GENESIS_TX, get_config(m_nettype).GENESIS_NONCE);
     add_new_block(bl, bvc);

src/rpc/core_rpc_server.cpp

@@ -1077,7 +1077,7 @@ namespace cryptonote
       return false;
     }
 
-    block b = AUTO_VAL_INIT(b);
+    block b;
     cryptonote::blobdata blob_reserve;
     blob_reserve.resize(req.reserve_size, 0);
     if(!m_core.get_block_template(b, info.address, res.difficulty, res.height, res.expected_reward, blob_reserve))
@@ -1148,7 +1148,7 @@ namespace cryptonote
     
     // Fixing of high orphan issue for most pools
     // Thanks Boolberry!
-    block b = AUTO_VAL_INIT(b);
+    block b;
     if(!parse_and_validate_block_from_blob(blockblob, b))
     {
       error_resp.code = CORE_RPC_ERROR_CODE_WRONG_BLOCKBLOB;
@@ -1216,7 +1216,7 @@ namespace cryptonote
         error_resp.message = "Wrong block blob";
         return false;
       }
-      block b = AUTO_VAL_INIT(b);
+      block b;
       if(!parse_and_validate_block_from_blob(blockblob, b))
       {
         error_resp.code = CORE_RPC_ERROR_CODE_WRONG_BLOCKBLOB;