auto_ptr → unique_ptr

Change the few occurrences of the deprecated `auto_ptr` to c++11 `unique_ptr`.
Silences the deprecation warnings.

Also add a missing `std::` for consistency.

src/miner.cpp

@@ -110,7 +110,7 @@ CBlockTemplate* CreateNewBlock(const CScript& scriptPubKeyIn)
 {
     const CChainParams& chainparams = Params();
     // Create new block
-    unique_ptr<CBlockTemplate> pblocktemplate(new CBlockTemplate());
+    std::unique_ptr<CBlockTemplate> pblocktemplate(new CBlockTemplate());
     if(!pblocktemplate.get())
         return NULL;
     CBlock *pblock = &pblocktemplate->block; // pointer for convenience