Make mining fee policy match relay fee policy.

This resolves a case in which a mismatch could be used to bloat up the
mempool by sending transactions that pay enough fee to relay, but not
to be mined, with the default policies.

Rebased-From: 037b4f1

src/main.cpp

@@ -51,7 +51,7 @@ unsigned int nCoinCacheSize = 5000;
 
 /** Fees smaller than this (in satoshi) are considered zero fee (for transaction creation) */
 int64_t CTransaction::nMinTxFee = 10000;  // Override with -mintxfee
-/** Fees smaller than this (in satoshi) are considered zero fee (for relaying) */
+/** Fees smaller than this (in satoshi) are considered zero fee (for relaying and mining) */
 int64_t CTransaction::nMinRelayTxFee = 1000;
 
 static CMedianFilter<int> cPeerBlockCounts(8, 0); // Amount of blocks that other nodes claim to have