Treat orphans as implicit inv for parents, discard when parents rejected.

An orphan whos parents were rejected is never going to connect, so there
 is little utility in keeping it.

Orphans also helpfully tell us what we're missing, so go ahead and treat
 it as INVed.

src/main.cpp

@@ -5156,13 +5156,29 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
         else if (fMissingInputs)
         {
-            AddOrphanTx(tx, pfrom->GetId());
+            bool fRejectedParents = false; // It may be the case that the orphans parents have all been rejected
+            BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+                if (recentRejects->contains(txin.prevout.hash)) {
+                    fRejectedParents = true;
+                    break;
+                }
+            }
+            if (!fRejectedParents) {
+                BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+                    CInv inv(MSG_TX, txin.prevout.hash);
+                    pfrom->AddInventoryKnown(inv);
+                    if (!AlreadyHave(inv)) pfrom->AskFor(inv);
+                }
+                AddOrphanTx(tx, pfrom->GetId());
 
-            // DoS prevention: do not allow mapOrphanTransactions to grow unbounded
-            unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
-            unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
-            if (nEvicted > 0)
-                LogPrint("mempool", "mapOrphan overflow, removed %u tx\n", nEvicted);
+                // DoS prevention: do not allow mapOrphanTransactions to grow unbounded
+                unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
+                unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
+                if (nEvicted > 0)
+                    LogPrint("mempool", "mapOrphan overflow, removed %u tx\n", nEvicted);
+            } else {
+                LogPrint("mempool", "not keeping orphan with rejected parents %s\n",tx.GetHash().ToString());
+            }
         } else {
             assert(recentRejects);
             recentRejects->insert(tx.GetHash());