Remove CENT-output free transaction rule when relaying

Remove the (relay/mempool) rule that all outputs of free transactions
must be greater than 0.01 XBT. Dust spam is now taken care of by making
dusty outputs non-standard.

src/main.cpp

@@ -760,8 +760,10 @@ int64 GetMinFee(const CTransaction& tx, bool fAllowFree, enum GetMinFee_mode mod
             nMinFee = 0;
     }
 
-    // To limit dust spam, require base fee if any output is less than 0.01
-    if (nMinFee < nBaseFee)
+    // This code can be removed after enough miners have upgraded to version 0.9.
+    // Until then, be safe when sending and require a fee if any output
+    // is less than CENT:
+    if (nMinFee < nBaseFee && mode == GMF_SEND)
     {
         BOOST_FOREACH(const CTxOut& txout, tx.vout)
             if (txout.nValue < CENT)

src/wallet.cpp

@@ -1232,9 +1232,10 @@ bool CWallet::CreateTransaction(const vector<pair<CScript, int64> >& vecSend,
                 }
 
                 int64 nChange = nValueIn - nValue - nFeeRet;
-                // if sub-cent change is required, the fee must be raised to at least nMinTxFee
-                // or until nChange becomes zero
-                // NOTE: this depends on the exact behaviour of GetMinFee
+                // The following if statement should be removed once enough miners
+                // have upgraded to the 0.9 GetMinFee() rules. Until then, this avoids
+                // creating free transactions that have change outputs less than
+                // CENT bitcoins.
                 if (nFeeRet < CTransaction::nMinTxFee && nChange > 0 && nChange < CENT)
                 {
                     int64 nMoveToFee = min(nChange, CTransaction::nMinTxFee - nFeeRet);