Patched copying of block headers so that auxpow is also copied. Fixes assertion crash when using SPV clients.

src/core.h

@@ -473,6 +473,7 @@ public:
         block.nTime          = nTime;
         block.nBits          = nBits;
         block.nNonce         = nNonce;
+        block.auxpow         = auxpow;
         return block;
     }
 

src/main.h

@@ -962,6 +962,7 @@ public:
         block.nTime           = nTime;
         block.nBits           = nBits;
         block.nNonce          = nNonce;
+        // AuxPoW is not part of the hash
         return block.GetHash();
     }