[Wallet] sort pending wallet transactions before reaccepting

During startup, when adding pending wallet transactions, which spend outputs of
other pending wallet transactions, back to the memory pool, and when they are
added out of order, it appears as if they are orphans with missing inputs.

Those transactions are then rejected and flagged as "conflicting" (= not in the
memory pool, not in the block chain).

To prevent this, transactions are explicitly sorted.

Author: dexX7

src/wallet/wallet.cpp

@@ -1482,19 +1482,29 @@ int CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate)
 void CWallet::ReacceptWalletTransactions()
 {
     LOCK2(cs_main, cs_wallet);
-    for (PAIRTYPE(const uint256, CWalletTx) & item : mapWallet) {
+    std::map<int64_t, CWalletTx*> mapSorted;
+
+    // Sort pending wallet transactions based on their initial wallet insertion order
+    for (PAIRTYPE(const uint256, CWalletTx)& item: mapWallet) {
         const uint256& wtxid = item.first;
         CWalletTx& wtx = item.second;
         assert(wtx.GetHash() == wtxid);
 
         int nDepth = wtx.GetDepthInMainChain();
 
         if (!wtx.IsCoinBase() && !wtx.IsCoinStake() && nDepth == 0  && !wtx.isAbandoned()) {
-            // Try to add to memory pool
-            LOCK(mempool.cs);
-            wtx.AcceptToMemoryPool(false);
+            mapSorted.insert(std::make_pair(wtx.nOrderPos, &wtx));
         }
     }
+
+    // Try to add wallet transactions to memory pool
+    for (PAIRTYPE(const int64_t, CWalletTx*)& item: mapSorted)
+    {
+        CWalletTx& wtx = *(item.second);
+
+        LOCK(mempool.cs);
+        wtx.AcceptToMemoryPool(false);
+    }
 }
 
 bool CWalletTx::InMempool() const