Replace use of BEGIN and END macros on uint256

Replace use of `BEGIN` and `END` macros on uint256 with `begin()` and
`end()` methods in the Merkle tree code.

src/merkleblock.cpp

@@ -53,7 +53,7 @@ uint256 CPartialMerkleTree::CalcHash(int height, unsigned int pos, const std::ve
         else
             right = left;
         // combine subhashes
-        return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
+        return Hash(left.begin(), left.end(), right.begin(), right.end());
     }
 }
 
@@ -109,7 +109,7 @@ uint256 CPartialMerkleTree::TraverseAndExtract(int height, unsigned int pos, uns
             right = left;
         }
         // and combine them before returning
-        return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
+        return Hash(left.begin(), left.end(), right.begin(), right.end());
     }
 }
 

src/test/merkle_tests.cpp

@@ -13,9 +13,9 @@ static uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vecto
     uint256 hash = leaf;
     for (std::vector<uint256>::const_iterator it = vMerkleBranch.begin(); it != vMerkleBranch.end(); ++it) {
         if (nIndex & 1) {
-            hash = Hash(BEGIN(*it), END(*it), BEGIN(hash), END(hash));
+            hash = Hash(it->begin(), it->end(), hash.begin(), hash.end());
         } else {
-            hash = Hash(BEGIN(hash), END(hash), BEGIN(*it), END(*it));
+            hash = Hash(hash.begin(), hash.end(), it->begin(), it->end());
         }
         nIndex >>= 1;
     }